I used ARC to go down to 3.2E from 4.2E.
It reported 1 Error, tried to connect as SU(Super User?) This failed.
Well, it finished flawless but when ARC came back up, it is saying that I have a region Sysmenu mismatch and where the current FW is displayed there is only a .
I just thought try it and booted back to sysmenu as I have BootMii boot2.
The sysmenu came up, checked version its 3.2E, fully working...
EDIT: BTW, all my installed VC games remained on the Wii also my savegames survived the downgrade...