There is no such thing as a "mod friendly" dealership. The dealer may sell performance mods, but if you have a problem that you want repaired under warranty, and the mods caused it, FORD will deny the claim and not pay the dealer for the repair. Now who pays?
Some dealers are worse than others - if you have any mod (say gauges) they'll freak and try to claim the problem is caused by them, but even the best dealer has no say if FORD won't pay them.