1) Only tickets booked with your miles will have the free redeposit.
2) Remember that if you cancel an award, that doesn't mean that it is available for somebody else. So if you book both with your miles and nothing changes, then you may be stuck with both tickets with your miles.
Also remember that just because a low award is available to you (as PM/DM) it might not be available to your SO (no status)
So, if while logged on as your SO you see a lower award, then yes, you could book it and then go back and cancel the one you booked with your miles.