Seems like it would depend on what your aftermarket radio supports, would need to be a unit designed control a changer. Might use Ford ACP protocol over the two "A" & "B" wires in addition to sending a turn-on signal on a different wire. If your radio doesn't have that, you'd have to research what is needed to emulate that, maybe with an Arduino. It does not seem as simple as hooking some switches up.
I don't have a changer, never tried, but here is a wiring diagram for it. I would sooner just use a radio with USB or a flash card input and use MP3 or flac instead.
If your radio doesn't have that feature, then I'd use a lighter outlet powered player, connecting to RCA analog input, or bluetooth, or even FM transmitted if it came to it. Those are now pretty inexpensive on Amazon. Some even link to your cellphone for hands-free calling.
