CRM uses the ActiveDirectory GUID AND the username to identify users in AD, so you can't remap the users manually (not without great effort and import anyway)
This might work:
Uninstall and remove Microsoft CRM from the server.
Detach the MSCRM_Config database and rename the datafiles (for backup)
Install CRM with a different organizationname than the one you are planning to use
Use the deployment tool to import the organization from the old data databasemapping to new users.
Best regards
Jens Egil Evensen