If I were to get a tune and a possible warranty issue were to arise... would reinstalling the OEM factory tune and then disconnecting the battery while I was installing my fog lights, remove all trace of an aftermarket tune?
We don't have the inside knowledge to confirm or deny this, so I'll have to defer to a conservative stance - if and when a Ford engineer were to dig in, it is entirely possible that they could find a trace of an aftermarket tune having been previously installed. But in terms of the quick and easy check that would be routinely performed by a dealer when a vehicle comes in for service/repair - checking the number of key cycles since the last ECU reset - there would not be any unique footprint of a tune being uninstalled vs. disconnecting the battery to install a fog light kit.