The problem is that the .atr file will contain the GUID of the old user and so the files will not be accessible to the new user. You will need to change all the permissions on objects to allow the new user to use the files you copied from the old user. You probably also need to do some search/replace for any username reference in the files.
So it's possible and can probably solve any issue manually, but I just don't see how (and why) you would like to make that in an automated way for multiple users.
.atr files related to UserID. Since you are changing user name, I dont think anything by User Name.
Just to understand, the GUID refresh won't work?( as we update dormant ids/passwords in catalog). Could you pl let me know.