A. After you've changed an AD domain to native mode, it remains in native mode. You can't perform an authoritative restore to change the AD domain from native mode to what it was before the switch (i.e., mixed mode).
If you haven't yet changed from mixed to native mode and believe you might want to switch back at some point, you should take one of the domain controllers (DCs) offline (thereby ensuring that it doesn't hold any of the Flexible Single-Master Operation--FSMO--roles), then perform the switch to native mode. Should you need to switch the AD domain back to mixed mode, perform the following tasks:
- Turn off all the DCs.
- Turn on the offline mixed-mode DC you set aside.
- Use Ntdsutil to give that DC all the FSMO roles.
- Rebuild all the other DCs from scratch; don't bring them online as DCs.
Be aware that some applications might have switched to native-mode compatibility and thus won't work when the domain is returned to mixed mode.