Sometimes you might want to provide local admin permissions to an Active Directory user.
This can be archived by different solutions:
Add an AD group to the local admin group (as described here)
sudo dseditgroup -o edit -a "DOMAIN\group name" -t group admin
Add the domain user to the local admin group
sudo dseditgroup -o edit -a usernametoadd -t user admin
More information can be found at the “Managing OS X Blog”
PS: Maybe you are also interested in how the change the ID of a user the right way.