I have a 20112 F150 that I bought second hand in June of 2019. The unlock did not work on the key/fob. I purchased after market keys and had the cut at Home Depot for less than $5.00 together. I then programmed both new keys by the standard method. This worked great!
Then I found out I could add remote restart by purchasing 11 thru 14 F - 150 OEM Genuine Ford remote Starter Kit from Amazon. It is plug and play, comes with 2 new keys for the remote start and installation took less than 10 minutes. I found a video on YouTube that helped.
After programming the 2 new keys, all 6 keys started the truck, GREAT! However the 4 old keys all worked on the fob, but the new ones didn't, I guess there is a limit to fobs, but not admin keys? I never did find a way to just delete 2 keys, but I did find the PATS service function in FORscan. This service procedure saved me from having to go to the dealer and pay big bucks.
Also the Forscan helped me to program my new Trailer Brake Control and the Remote Start.
I'm only a beginner here but what I have read is:
You can only program 4 fobs and if you want to delete keys you need to delete all the keys and then reprogram the 4 new ones.
But like I say I'm a newbie here and just learning..... So if I'm wrong don't shoot me down....