For 32-bit its not as big of a deal to change the first user / disaster recovery user.
In 64-bit I don't recommend it as there are a lot of hooks into the underlying hostOS and AAA sysadmin GID/UID and profiles that can easily get messed up.
I would recommend just creating a new user with same rights and just not use the old one, it is asking for trouble to try and change the host OSs root/first/disaster recovery user.
Some notes from when people have tried this, with success sometimes.
++If the first user is deleted in Sysadmin - the user will not be deleted in HostOS. Credentials will remain in HostOS.
++ First User’s password change on Sysadmin will always sync to HostOS.
++ If the disaster-recovery user is unconfigured then the next first user will get synchronized to HostOS.
++ The user on HostOS doesn't get deleted. At any time it will have either the first user or disaster recovery user.
++ We can delete the first user and create a new one. But We cannot delete the first user when other users are configured.
++ To delete the first user all other users have to be deleted first.
++ If the first user is not created again in sysadmin-vm (means no users on sysadmin-vm), a user from XR-vm, in the order of their configuration, automatically gets synced to sysadmin-vm, only when there is user add or delete config operation on XR-vm.
Sam
