Some instances of Commander Shepard are embarking on Mass Effect 3's climactic campaign with some alterations. The galaxy's most important (and most imported) face is not being properly preserved in the transfer between some games of Mass Effect 2 and Mass Effect 3 (ours included), prompting BioWare to work on a correction.
According to BioWare's Community Coordinator, Chris Priestly, "The issue is likely in how faces were detected when imported from Mass Effect 1 into Mass Effect 2, and we're working on the best way to correct it for affected players." In our experience, a wonky import process only messes with facial data, and none of Shepard's recorded actions throughout the previous games.
If you're driven mad by inconsistent canon -- or can't bear the thought of Shepard being vain enough to get some touch-ups before his last stand -- BioWare is pointing you to a set of user-made tools for the PC version. As far as we know, this is the only time we'll ever recommend DIY facial surgery.