I would say that whether you potentially void your warranty is contingent on whether you have wiring in place, more so than whether you have a hitch platform in place (i.e. either a 1-1/4" square receiver tube or a flatbar receiver arrangement). Once you have wiring in place, it is pretty evident that you are towing a trailer. Otherwise, lots of folks use hitch-mounted bike carriers...
If you want the capability of a 1000# trailer (and therefore need the writing) -- I would say the following: If you have the vehicle serviced by Ford, I would say that it is problematic. If it is serviced by others (including yourself) probably no-problem.
If it were me, I would grab the wiring take-offs (for brake, ground, parking lights) from inside the car -- under the rear seat (assumedly the wiring loom passes that way). Make tie-ins, and then use factory-type Molex-like connectors. I would make it such that if you had an engine or transaxle related warranty claim where you would have to approach Ford, you would disconnect the wiring at the takeoff points prior to bringing in the car. Goodness knows, no-one would search for said wiring takeoffs there in the event of awarranty claim.
I don't advocate running the car in a manner that challenges its ability to deal with 1000# of trailer, breaking it, and then expecting Ford to pay. However, with intelligent use, 1000# max would probably be fine (750# would be better).
Remember, Ford will not pay for your clutch, regardless (it's considered a wear part). I would also be careful not to be on the gas, much (rather, coast, instead) when the wheels are cranked over right or left (that's hard on the CV joints). For that matter, goosing it, with the wheels turned much, is hard on the CV joints, regardless of trailer or not.
As for me, I once-in-a-while use my 500# empty trailer for runs to the trash and yard-wastes dump; 250# max payload, downhill all the way... I don't want a mfr telling me how to go easy on my car (I know how to do so).
Tell me if 750# total trailer wt is much different than four 200# people in my car?
Eurofordfan