There really isn't a need to replace the entire seat assembly. Pulling the seat covers off and putting the correct one on is a simple job. I watched a guy do it in the pits at the drag strip on his Mustang in between passes.
No reason to believe that the dealer can't do as good a job as the assembly at the place that put them together (they aren't done on the Ford assembly line, they are from a supplier and shipped to Ford to install). Like I said, if it can be done in the pits between passes on the drag strip it really isn't that difficult to do correctly.
Perhaps you are having buyers remorse and this is a good excuse to get out of the deal?
No offense, but for almost $40k, I should get a car that comes as it was supposed to from the factory. Why would a guy be changing seat covers in between passes? Either way, it might not be a hard job, but you can't convince me that a guy at a dealer who does a handful of these a year will be able to do as a good of a job as a supplier who probably does hundreds a day, has all the right tools, the right training, quality control, inspection, etc. It shouldn't be that hard to get a finished seat base from the supplier and swap it out.
As for buyers remorse:
This is the first car I ever ordered exactly how I wanted it equipped. It's been the background picture on my computer since June. It's my facebook picture. I had my car all cleaned up and cleaned out, ready to trade in. I had my title, my loan, etc. I was ready to swap keys, sign papers and go. I arrived at the dealership to find my car has a gay pinstripe on it. The sales lady doesn't seem to care that her bracelet is banging against the car as she puts the antenna on. I discover that it has the wrong back seat. The dealer wants me to bend over on my trade in. I understand it's business, but I'm not going to give my car away. Needless to say it was an all around disappointing experience. Do I want this car? Yes. Do I need this car? No.
I sold my Cobra in June, I pulled the trigger on this car on the last Friday of June, the order did not go in until the first Monday of July. I hoped to get it in early to mid August. The car did not arrive until the last Thursday in August. Due to the holiday weekend, etc, I didn't get there to pick it up until Tuesday after Labor Day. Now it's approaching the middle of September. The summer is over and winter will be here soon. If they want to fix the problem and give me a fair deal on the trade, great, I'll take the car. If not, I'll walk away from this one and order another one from another dealer. At this point, it doesn't matter much if I get the car now or in the spring.
Call me crazy, but I don't think I'm asking too much that a new car should be built right. If not, it should be fixed correctly.