Great write up!
FWIW, re “tape the pin” on the MC7455 is needed ONLY if the Mikrotik miniPCIe support does NOT support USB 3.0. Not a definitive list: basically older RBs, SXT, & top-slot LtAP WOULD require taping (not a complete list) since the miniPCIe bus only supports USB 2.0. Stuff like wAPacR, LHGR, Audience, and bottom-slot LtAP all support USB 3.0 – those would NOT require taping. Search for postings from @SiB and your model number, since Mikrotik website isn’t helpful on which models use USB 2.0 or USB 3.0 with their miniPCIe slots – but that’s why you may, or may not need to cause the MC7455 to be recognized as a USB device on USB 2.0-only RouterBoards.