Bean, emanuela - it just means underwear, right? I think emanuela was being a bit figurative when she
applied that broader meaning, but I could be wrong.

Well, it wanted to be a joke, but not only.. I mean that the meaning seems really come from the need of changing underwear, but now it is hidden and forgotten - and no, we don't say mutande for everything that has to be changed, even if it would work , as adjective: le cose mutande = things that have to be changed.