No, if you use unlock/debrand your phone to get the last update, then your zune should have phone backup. If you restore the phone to last backup it will put your phone back to pre-NoDo stage (7008 Feb Update). From that point you can again unlock / debrand your phone but this time either edit the register to prevent the phone from relocking or download that Samsung Tool app. If you want the phone to relock then don't edit registry but use the Samsung Tool (assuming you have Focus here).
Unlock / debrand again to get No Do then used the app to rebrand your phone if you really worry about having problem. The phone will be rebrand for if and when At&t release their official update.
Or if you don't want to do all that you can just keep using phone as is until At&t release update and you can again use restore point. Problem is you will loose all the new stuff you install since the last backup.
I hope I am not confusing you even more.