Q: Modifying Yosemite (10.10.5) to use Magic Trackpad 2?

Magic Trackpad 2 requires El Capitan to function properly.   Older macs, provided they are upgraded to El Capitan, will in general work. though I cannot say how old.   But the key is El Capitan.

Yes.   That was what I implied.   Don't forget to tell us how it performed after the update.