Problems with change sql permissions after migrating domain user/group accounts into root domain

I have a root domain and child domain.

After using ADMT to migrate the domain user or group into the root domain, when I use enterprise manager to try and change the permissions allocated to that domain user/group, i get the 'Error 15401 NT user or Group not found'.

This is a correct error as the user is now in the root domain, however sql (in sysxlogins) still thinks its in the child domain.

Is there a simpler way, other than collecting the users permissions, deleting the user from SQL then adding back in with the correct domain\username format, then adding the permissions back?

I tried renaming the 'name' in sysxlogins (not recommended) and while that worked, whenever I tried to add the migrated user to another database, the login name was missing and would not resolve.

I believe it is something to do with the SID not matching.

Any ideas on how to fix this ?

You're correct, different SIDs.

Here are some articles that may help.

http://www.sqlservercentral.com/columnists/cBunch/movingyouruserswiththeirdatabases.asp Moving Users
http://www.support.microsoft.com/?id=246133 How To Transfer Logins and Passwords Between SQL Servers
http://www.support.microsoft.com/?id=298897 Mapping Logins & SIDs after a Restore
http://www.dbmaint.com/SyncSqlLogins.asp Utility to map logins to users
http://support.microsoft.com/kb/274188 Troubleshooting Orphan Logins