I have done this enough times, but just for documentation sake.
So, you get a cool new OS (Windows 8 Release Preview maybe?) and you repave your machine. You want to add to your domain over VPN and then login with your domain creds. Now, you must have an account that has access to add computers to the domain, of course, but this is what you do.
Why would you want to do this? Well, if you are telecommuter, it might be something you run into. If you want to redo your machine at night and not waste time during the workday, is another reason. If anything, it isn’t that complicated, but it could be confusing if you have never done it before. If you have a basic understanding of windows networking and Active Directory you should be able to get what is going on here.
1. Repave your machine!
2. Set up machine with new name
3. Install VPN, connect to your network.
4. Add your machine to your domain as you would when on the LAN network.
5. DO NOT REBOOT. I repeat, DO NOT REBOOT. Even though Windows wants you to!
6. Go to user management and add the domain user you want to login as to the local admin group.
7. Now, feel free to reboot.
8. Drink a beer.
9. When the login screen comes up, login as your local machine account that you setup when you repaved your machine.
10. Connect to VPN.
11. “Switch Account” back to login screen (VPN is still connected!)
12. Login as the domain account from step #6.