The "stay mashed" property is by design for these types of earplugs because they are meant to go right into the ear canal. The idea is you mash them (well, carefully roll and compress) then insert them while still mashed, holding them in as they slowly re-expand.

But this is, of course, to ensure protection in the case of dangerously high sound pressure levels. Cutting them would also compromise them in this regard. Perhaps different if you are using them to block out low noises for sleep.