Some use cases require a wtdocument within Windchill is renamed. However, for traceability and uniqueness, the Windchill identifier should not be changed. Currenlty, we do not have this function in Windchill 9.1.
Ideally, a user should be able to rename a wtdocument, however, be restricted from editing the number of the same wtdocument given certain policy being applied/denied to/from their role in the ProjectLink or PDMLink context.
See Case #11235224, opened with PTC Technical Support on 2/7/2013.