I dont have any updates right now, but I just figured out something that has plagued me for awhile and thought i would share.
Normally when I want to change the uvs on my model I export to maya do them there, and try to reimport it into subdivision level 1 of the ztool. Sometimes you get lucky and it works, but most of the time it turns into an exploded mess, and morph targets cant fix it. The method I used to use to get around this was to create a clone of the original and project it onto a fully subdivided tool with the new uvs - this would still be really difficult because complex areas tend to get screwed up in the projection, and you would have to spend a long time fooling around with it just to get back to what your original tool was like.
K here is what I found (see the original post here: http://www.simplycg.net/viewtopic.php?f=22&t=5051 )
get the classic version of uv mapper (free) at:
http://www.uvmapper.com/downloads.html
open uv mapper
import your original model before uv change
import uvs of the new model after uv change
export model
open zbrush
import model at subdivision level 1 of your tool
your tool should be update with the new uv’s and all detail and subdivision levels will be preserved. I think this works because uv mapper is keeping the original point order instead of creating new ones.
Sorry if you all already know this, but hopefully someone who is also struggling with this issue will figure it out.