Honestly, you could just hit us up here and we could handle it. PMs are a marvelous thing!

I could handle this today if you PM a phone number for the account.
Here's an idea: Tell them you want to replace the 722 with the 612. If they allow you to do that swap -- I think they will -- obviously disconnect the 625 and put the 612 in it's place. When it works, call in to tech support and tell them what you want to deactivate and what to activate. You might be able to deactivate/activate online but they might have the receivers tied together as to which is going away and what-not.
Switching which box is coming back mid-exchange would guarantee a charge ($300 bucks). Takes about 30 days to show and a LOT of people get gigged on that. No CSR would reverse it until the proper box shows up.
CSR can change what is meant to be deactivated. Just because you toldcem one thing on the phone before doesnt mean a later call cant change it.
Yes, it actually does. I see this happen all too often. Trying to circumnavigate the system leads to more hassle for you as the customer.
I think I recall someone saying that the "policy" is that since you're going from SD to HD, a visit is req'd.
With HD already on the account, there is a way to do it rather easily.
Probably have to sign a 2 year agreement, and at this time that particular agreement is not online, but either hard copy or on the FSS's (installer) tablet pc.
They will ship the contract with the box. So long as you accept the Terms and Conditions, its a done deal. Again, my teammates and I on the threads can handle this for you, no glitches or hangups. Ask any number of the people we have helped upgrade just in this forum alone.