Or turn their face into mush! (See Minority Report or, for that matter, practically any Spielberg film.)
Seriously, though, I think the idea of a gradual evolution of the individual cells comprising an organism is somewhat feasible, just not instant facial modification. I'm thinking something along the lines of Bungie's Oni, in which people are seeded with hyperevolved versions of themselves which gradually replace the basic human cells as they divide.
Immediately useful applications seem to include resetting of the Hayflick Limit (essentially acting as an elixir of youth, returning a person's body to a healthy 20 years old) as well as those which Tomoe has already described. Realistically, though, this process would take several months or even decades, in the case of extreme alterations, rather than days or weeks. I'd expect the ID-SOL to have originally been produced in this manner. So, yeah, it would be easier to just grow a new body, but if the risk is minimized (and Tomoe's statistics seem inflated to me) then it could provide a low-cost alternative to the low end of the socioeconomic spectrum (and the criminals.)
It is unlikely that any such process could be initiated by a handheld device, but then again, who knows?