You can do what you want, but it is a very bad idea.

Much better is to document what drives are going to be needed across your organisation, assign a drive letter to each and ensure that the drive mappings are consistant.

Now your script becomes simply:
Code:

If in group X
  Map G: \share
EndIf
 
If in group Y
  Map T: \othershare
EndIf
 
...and so on ...


It would be highly unusual to need have the same share mapped to different drive letters.