Well, now that you asked. Yes you can rollback, but you should be warned, and I just found this out. If you use the custom FW on the Plus you may lose Netflix depending on the official version of the firmware that you have now.
I’m not sure if this is on just the custom firmware that has not been officiall released yet (which is 1.05.04_B) or if it’s also for the 1.03.49_B-WDLXTV-Plus-0.4.7.3 [flash]. I only have a Live and not the Live Plus so I can’t tell you for sure.
I do know that this was not and issue previously and is something that was just implemented with the newer WD firmware.
So just remember you are doing this at your own risk.