Creo Imaginem and Perdo Imaginem explictly state they can affect all 5 senses; the same seems to be true of Rego Imaginem, which just refers to "one sense" in the guidelines.
Illusory touch is described as the sensation of touch, but if someone pushes past the sensation their hand will go straight through the illusion.
Based on this, I'm puzzled as to why the Muto Imaginem at the highest guideline says "change the object completely, in all things except touch." (ArsM5, p. 145). Why this specific exception for Muto? If I make a box look like a bale of hay, why can't I make it so someone touching it will feel hay? Is this an intentional exception, or an unintentional one created by poor wording that needs errata?
I also note that none of the example Muto Imaginem spells create an illusion of a different size than the target. In fact, Image Phantom, page 146, seems to explicitly forbid it - "The illusion cannot be cast on things that have a shape or size improper to the final appearance". Does this mean the exclusion of touch in the guidelines is intentional, because Muto Imaginem can only ever change the surface appearance of an object but not its size or overall shape? But if it can't change the size, what Technique would be used to make a man look like a giant or a dragon? If it can, what are the guidelines for illusory size change using Muto Imaginem?
Ah yes, not sure how I missed that because I read that spell description. This suggests that the "in all things except touch" is poor wording or just an error.
And doesn't resolve the question about size, as Disguise of the Transformed Image also makes it clear the person must remain "passably human".
That spell has a base level of 4, at which you can only change 4 sensations of the object.
Nowhere does it say that MuIm can't change the touch sense, only that level 5 spells can't do it according to the guidelines.
Of course, that leaves open the question about what the difference is between the guidelines for level 4 and level 5. The level 5 guideline does not seem to allow more than the level 4 one.
I like the idea that only 4 senses can be changed at once: it might be looked as a flaw in Hermetic Theory, though I like to think that something deeper is going on and that for some reason the illusion needs to keep a link with reality, and that that link is the unchanged sense.
Regarding to size changes, not allowing them is actually a way to avoid the troubles that the mismatch between the real target and the resulting illusion. For example if you reduce your size low enough (to the size of a fly or an ant, or maybe something bigger), you would be pretty much casting an invisibility spell. That being said I don't see any trouble including size change magnitudes, if you just make sure that MuIm base 1 to change how something looks needs enough size modifiers to be worse than PeVi base 4 that renders something invisible. It is ok to have two ways to do something, as long as the convoluted way is less practical than the obvious one.
Hmm. ArM5 p.145 box Muto Imaginem Guidelines has as its important introductory first phrase:
These are useful and powerful illusion spells, altering the visual image, noises, smell, or taste of some object or being. The image remains altered without your concentration and adapts itself appropriately to the medium.
As an erratum for these important lines never happened, this strongly suggests, that the exclusion of touch there is intentional. This would make the level 5 guideline indeed a needless copy paste error from e. g. the p.144 box Creo Imaginem Guidelines.
Sticking to the lines above, p.146 Disguise of the Transformed Image would have to be errataed to:
Makes someone look, sound, taste, and smell different, ...
ArM5 p.146 Image Phantom
The illusion cannot be cast on things that have a shape or size improper to the final appearance.
works well with the current MuIm guidelines, because making relevant parts of a thing appear or disappear is PeIm or CrIm.
This distinction is important especially, because MuIm is easier to cast and adapts better to changing images than PeIm for sight. Also, things made invisible still cast shadows and thus require special attention in spell descriptions - which is not given to MuIm spells.
Perhaps, but it seems very odd if MuIm can't affect the sense of touch when CrIm, InIm, and PeIm all treat touch as no different than the other senses.