I can't remember much except that Tony fakes his own death (it was Tony/Steve) because his life is under threat (Hammer? not sure) and he has this elaborate plan set up whereby he reappears i a different suit as a woman, pretending that this person was a mutant with a virus liquifying her body and also if she if ever not it in the suit she would unleash a virus that would kill mutants (or something like that). Wearing the suit full time actually causes Tony a lot of pain but he kind of pushes that into his role...and also maybe pees in a corner at one point because he gets caught short at the mansion although that might have been a totally different story.
Anyone remember this one at all?
EDIT: FOUND! FFS I've been looking for it for three days I post this and WHAM find it: Even the Light is An Illusion by Mizzy at AO3
EDIT II: Er I've tried to remove the status:not found tag thrice now so if it is still there I am really sorry!