So far, everybody is right.
You can hookup alternate power ...
or just reset a few things when you're done. Window reset takes about 30 seconds. Resetting radio presets shouldn't take long. The ECM's adaptive tuning params will be lost but will be relearned in a few minutes; any custom tune will still be there.
Personally, hooking up alt power is more trouble than resetting a few thing. YMMV.