Transfats and cell membranes -- do the cells repair the damage? Or are the molecules forever "mutated" ?

Yeah, cells constantly do recycle their membranes, so eventually those phospholipids will get used in vesicles or such. Also, i don't think changing the shape of a few phospholipids will affect it that much, unless the entire plasma membrane is in a different shape phosphlipid, which would screw up the fluidity of the membrane.