To program additional Remote Start (RS) FOB:
I purchased a 'Lincoln' emblem 1 way RS FOB (not programmed of course) on EBay. Difference between this FOB and original was that the EBay FOB Lincoln emblem was upside-down, so as on the orig. to read "Lincoln" the light would be on upper side of remote: On the EBay RS FOB the light would be at the bottom.
So here is how I programmed the additional Remote Start FOB so it would work with my MKZ:
Have key ready with the RS FOB separated but handy because you will need to use it in the process
1. With doors closed/locked and windows up insert Key and turn to 'on' position (just turn on, do not start vehicle)
2. Press & hold program button and brake peddle down simultaneously until you hear 3 short horn beeps (could take 15 seconds or so) then RELEASE button and brake peddle. The beeps verify that you have entered Programing Mode. NOTE: Key is still in 'on' position.
3. Press & hold button ON THE REMOTE START FOB YOU WANT TO PROGRAM until you hear one beep.
4. Turn key off and remove. DONE