I don't get what's so new and different about this downgrade method? Myself and others did the MC swap thing with the 1.50 upgrade a long time ago:
I stopped trying when the 1.50 update would say the installed firmware is newer. Those that have managed to bypass that and force the update to run have bricked their PSP's. Running the 1.50 update on a newer system is not the solution to downgrade.
I've also tried the MC swap with the US 2.0 (as I run Jap 2.0 now) and receive a message that it is the same version as installed.