This theory is a thorough study of using the Power as a disguise, and what the implications are for Forsaken who disguise themselves.

First, there are four major weaves with subtle differences described in the series that allow one to change their appearance:

1. Illusion (White Tower version)

Illusion is a weave taught at the White Tower. In LoC, Alanna uses this weave to impress novices: Alanna stood in the middle of the common room unchanged—to Verin, at least—but the Illusion's head touched the ceiling beams.

Obviously, this is the same weave Moiraine used in Baerlon to fool Whitecloaks in tEotW, as Rand recalls: They think to impress me spinning the Mirror of Mists? Lews Therin's incredulous laugh faded into mad giggles. Rand did not need the man's explanation; he had seen Moiraine do something like this once. Asmodean had called it the Mirror of Mists too, and also Illusion.

Which leads us to the second weave...

2. Illusion (Age of Legends version), also called Mirror of Mists.

This is similar to the White Tower's version of Illusion, except for two things: the weave is inverted, making the disguise undetectable to channelers as well, who might otherwise see the glow of saidar. A second weave is also used to hide the ability to channel, making the disguise complete.

In tPoD, Alviarin believes Mesaana must be using the White Tower's version of Illusion when in fact it is the AoL version: Alviarin flung herself from her knees onto her belly before the woman who seemed made of dark shadows and silvery light. Seizing the hem of Mesaana's dress, she rained kisses on it. The weave of Illusion—it must be that, though she could not see a single thread of saidar any more than she could sense the ability to channel in the woman who stood over her—did not hold completely, with her frantically shifting the skirt's edge. Flickers of bronze silk with a thin border of intricately embroidered black scrollwork showed through.

And again in CoT: Silver eyes frowned from a face of smoke, with silver lips drawn in a tight line. It was only Illusion, and really not done any better than Alviarin could have. A flash of green silk skirt embroidered with elaborate bands of bronze showed as Mesaana glided across the Domani carpet. But Alviarin could not see the weaves that made the Illusion any more than she had felt those the woman had used to arrive or cast the room in shadows.

Elayne and Nynaeve also use the AoL version learned from Moghedien who still uses her own disguise to pose as Marigan: Not with all of their "discoveries" coming from Moghedien. There had been a good many, beginning with "inverting," so a weave could not be seen by any but the woman who had woven it, yet they had not passed everything on. How to hide your ability to channel, for one. Without that, Moghedien would have been unmasked in hours—any Aes Sedai within two or three paces of a woman could sense whether she could channel—and if they learned how to do that, they might learn how to penetrate it. And how to disguise yourself; inverted weaves made "Marigan" look nothing at all like Moghedien.

Some limitations are also revealed: In truth, no one gave her and Birgitte a second glance, though Birgitte's aged face was often challenging and she herself was tall for an Ebou Dari woman. That was what they saw, by way of not so simple weaves of Air and Fire that Elayne had inverted and tied off herself. When Elayne looked at Birgitte, she saw a woman with fine wrinkles at the corners of black eyes and black hair touched with gray. The disguises were easier the closer you stayed to how a person really was, so the hair flowing down Birgitte's back, tied in four places with tattered green ribbon, was considerably longer than Ebou Dari women wore it, but then Elayne had not cut her hair either, and no one seemed to pay it any mind. It was a perfect disguise; she just wished she did not have to sweat as well. With the addition of the even more complex weave of Spirit that masked a woman's ability to channel, Elayne had walked right by Merilille on her way out of the palace that morning.

We get to see Forsaken's POV about this weave as well: His skin tingled slightly as she channeled, and for an instant her image changed. Her skin became coppery but dull, her hair and eyes dark but flat; she appeared gaunt and frail, a once-beautiful Domani woman slowly losing a battle against illness. He barely stopped his lip from curling. One touch would prove the angular contours of that face were not hers—only the most subtle use of Illusion could pass that test—but Graendal seemed wedded to flamboyance.

More limitations from Nynaeve's POV: Illusion worked best the closer you stayed to what was there before, in shape and size at least, so bits of the Ebou Dari dress flashed through the Domani garment as Elayne whirled to examine herself in one of the room's two large mirrors. She laughed and clapped her hands. "Oh, he will never recognize me. Or you, near-sister."

So we know that the more you deviate from the true shape and size of something, the harder it is to keep the disguise perfect. Mesaana's dress shows because it looks nothing like the shadows and light disguise Mesaana has adopted. Elayne's Ebou Dari dress shows through the Domani garment because they have different shapes, a difference further enhanced by Elayne's rapid movement. Graendal's face and the elderly Basene's have different contours, so her disguise could be penetrated as well.

It would be easy to weave a disguise, and then wear the appropriate clothing to complement it, as Elayne and Nyaneve do in Ebou Dar, to reduce chances of being discovered. Not changing hair would also aid, as shown in the above quote about Elayne. Elayne's disguise adds age marks such as wrinkles, a very subtle change unlikely to be uncovered unless someone is actually touching their skin. If she were to keep her true age showing, and only darkened her skin to an Ebou Dari tint, the size and shape would not have changed, and this would qualify as "the most subtle use of Illusion" that "could pass that test" of not being revealed by touch.

3. The Mask of Mirrors

It is unclear whether the Mask of Mirrors differs from the Mirror of Mists (AoL Illusion). All mentions of it are included below.

Watcher POV: Graendal maintained the Mask of Mirrors that hid her true form, but Sammael had dropped his, golden-bearded again and just head and shoulders taller than she.

Graendal POV: Or maybe at something beyond. He still held the Mask of Mirrors, giving him the illusion of added height. She had dropped hers as soon as the gateway closed.

Rand hides his Choedan Kal: At least once every day, though he had promised himself he would not, he lifted the massive wardrobe of polished blackwood and ivory in his bedchamber, floated it aside on flows of Air and carefully unraveled the traps he had set and the Mask of Mirrors that made the wall seem smooth, all inverted so no other eyes but his could see.

Rand appears as Nuli: Mistress Harfor gaped after Min until she vanished around a corner, then gave her tabard an adjusting tug it did not need. She turned her disapproval on Rand. Even with the Mask of Mirrors she saw a man who towered over her, but Reene Harfor was not a woman to let a small thing like that put her off stride for an instant. "I mistrust the looks of you, Nuli," she said, her eyebrows drawn down sharply, "so you watch your step. You'll watch it very carefully, if you have any brain at all."

Sammael did his best to stay more than arm's reach from Sevanna, which probably indicates that his added height disguise would be disrupted by a touch.

4. Lanfear's disguises

Lanfear adopts a disguise as Keille Shaogi, a very fat woman: The only woman in sight beside Aviendha and the Maidens was walking up from the second wagon, but she certainly did not match that voice, one of the loveliest he had ever heard. Rand frowned at her and shook his head, and he had cause. A foot shorter than Kadere, she must have weighed as much or more. Rolls of fat nearly hid her dark eyes, disguising whether they were tilted or not, but her nose was a hatchet that dwarfed the peddler's. In a dress of pale-cream silk stretched tight around her bulk, with a white lace shawl held above her bead on elaborate ivory combs thrust into long, coarse black hair, she moved with incongruous lightness, almost like one of the Maidens.

Yet Lanfear's disguise, obviously a major change in shape and size and not at all subtle, is not disrupted by touch: Keille watched, round face unreadable, until the white door closed, then suddenly rounded on Mat, who was on the point of slipping away. "Few men have ever refused an offer from me once, much less twice. You should have a care I do not take it in mind to do something about it." Laughing, she reached up and pinched his cheek with thick fingers, hard enough to make him wince, then turned in Rand's direction.

Either Rand and Mat are truly not perceptive (which is odd since Rand suspects either Isendre or Keille might be Lanfear) or Lanfear's disguise doesn't have the same limitations as the other weaves we've described.

Conclusion:

Lanfear's ability allows for the possibility that a One Power disguise may exist that alters one's size and shape with no chance of disrupting the weave by touch. If Lanfear knows such a weave, there is a distinct possibility other Forsaken may know it as well.

Alternately, it seems obvious that any One Power disguise that does not alter one's size and shape is subtle enough to pass the test of touch without being discovered. Weaves to alter the size and shape of a person or clothing can be detected through touch or simple movement, with the possible exception provided by Lanfear.

For your reference, I've listed below every use of One Power disguises I could find, both confirmed and possible.

1. Moiraine at Baerlon

2. Lanfear as Selene

3. Lanfear as Else

4. Rahvin as Gaebril

5. Sammael as Lord Brend

6. Be'Lal as High Lord Samon

7. Lanfear as Keille

8. Asmodean as Natael

9. Moghedien as Gyldin

10. Moghedien as Marigan

11. Graendal as Basene

12. Demandred as Taim

13. Alanna in Caemlyn

14. Nynaeve, Elayne, Aviendha and Birgitte as Ebou Dari

15. Aes Sedai at Rand in Caemlyn

16. Rand hides Egwene in Cairhien

17. Sammael as Caddar

18. Graendal as Maisia

19. Rand hides his ter'angreal

20. Mesaana as a mysterious woman of Light and Shadows

21. Rand as Nuli