If you de-badged an Ascari KZ-1 that theory would work...
But if you de-badge a Focus, you're likely parked next to another one when you go -literally- anywhere in North America, so you're not fooling anyone.
I think the long & short of it is that if you wanted a special car that no one would recognize, you should have bought one.
OBVIOUSLY you can do whatever you want with your car, but trying to pass it off as stealth or ambiguous is really silly in my opinion. Disassembling, filling, shaving, priming, painting, and reassembling the trunk lid just to remove the Ford emblem is a lot of work for a modification with zero substance. I'd suggesting putting your effort elsewhere like a tune or decent suspension setup... You'd enjoy them more and you wouldn't have any reservations about doing them like you are having with this trunk dilemma.