Hope you have fun. I'm just finishing some boots for the pre-teen using that method (I selected just feet and toes in poser when exporting, then imported as a single vertex object). It is mildly annoying that you can't put a vertice or mesh "off limits" so you can see it but not accidently move it. But lots of selecting by name kept me from getting too much cross-talk. Two tricks I used with some degree of success; one was to start the new mesh large and lower it towards the surface of the foot. That made it easier to select. Also, in the gourand mode, I could tell the moment it "penetrated" or started to go inside the other mesh. The other trick was to select all of my new mesh and "crease edges." Since Carrara marks the creases a nice blue or yellow, it was easier to see which mesh I was about to grab and manipulate (the original figure, or the new clothing).