I'd like to create one model that I import into an XNA game. 

I'd like to be able to copy this model and make programmatic modifications to it during execution (with the intent of using the same model to represent multiple characters in the game). For example, I'd like to make the legs slightly longer or shorter, or the waist slightly fatter or thinner, or the head slightly smaller or larger. 

I know how to use transforms to modify a mesh, but it seems that what I need here is to apply a transform to only a subset of vertices in that mesh. I have no idea how to do this in XNA, or if it's even supported. 

Two questions:
 1) is functionality like this supported in XNA?
 2) if so, what kind of methods are used to obtain the desired result?

(note, this was crossposted from stackoverflow, this forum was recommended as a better place for my question)