Incorrect. The Act covers warranties on repair or replacement parts in consumer products, there is no distinction for OEM and non OEM.
Law aside, it is always in the best interest of the dealer to cover warranty items. Primarily it is the good will to their customers, but secondary, Ford does pay them for the work and it is an opportunity to sell more work to the customer. If the modification clearly did not lead to the failure, Ford WILL cover it. The dealer does NOT want to go to court any more than you. The consumer also has the advantage of the office of consumer liaison that every manufacturer has in house to advocate for them.
Mod away, just be aware if your mod leads directly to another failure it may not be covered. other than that is is required by law to be covered.
So much fail here.