this question has been asked over and over. Warranties are not "black or white", there is a LOT of gray area in there. Your dealer and/or Ford can decline warranty service for any aftermarket part. Don't pull the Mag-Moss act here either because Ford has more lawyers and cash than you or I do.
Dealers make less money from Ford on warranty work, and there is a ton of paperwork and processes to do to complete it. You think they "want" to go through all of that when they can charge Becky full list price on parts and labor for her repairs? Not much room to park the cars waiting on parts either.
This said, some dealers are more friendly than others. On top of that some service advisors at a given dealership are more picky than others. Don't go to your dealer and say "well Jim-Bob from this Facebook group I'm on said it doesn't void the warranty".