I am currently reading 'Gurps 4th Magic' and the spell 'Illusion Disguise' just says that you have to create a basic illusion and then use 'Illusion Disguise' to superimpose it.
However it never talks about the wearer. Could he just resist it? I can imagine a few situations where it is useful to put an illusion on someone. For example to discredit them in front of a crowd etc.
So, is there a rule that stops them from just putting it on anyone they want or would that fall into houserules?