they should be ok with mailing it, however they will mail it to where you "moved" to, so make sure your "home". Enough said.
If all else fails, call in and say its defective, and you want a replacement shipped to you, if you dont have the protection plan there is a 19.99+tax shipping and handling charge, but you can argue that away. Also this will not extend your contract but make sure the csr notes the account with whats going on. "the box doesnt power on" is usually a good line to get a new one. If you have swm you can blow it up (not literally) by hooking the power inserter up backwards and sending voltage into the box, but Id just claim it doesnt work and have them send you a replacement. The chances of you getting a hr20 again are slim and none. The box hasnt been made in years and is not currently being installed.
Another option, but costly to you, is a customer owned box off ebay. Doing so you can replace your existing box yourself, and own the new one. This way if you ever deactivate you can reactivate without returning your equipment.
http://www.ebay.com/itm/Directv-HR2...US_Satellite_TV_Receivers&hash=item1e7ac03c2a
250usd buy it now, rid number is listed call directv to verify
http://www.ebay.com/itm/Directv-OWN...US_Satellite_TV_Receivers&hash=item3cd1a21ac1
150usd bid (as of current) pm seller to check rid.