Questions about backup

[Joeteck]

OK, I rooted my phone.

Went from 2.1 to Froyo 2.2 virgin. (Build FRG01B).

I did the backup of my original ROM to the phone. I want to switch to the Bugless BEAST V0.4, however I don't want to clear out my original backup.
Can I just clear cache and wipe user data, and then install the ROM via update.zip?

Also, I bought SetCPU, once I wipe the phone will it let me download the file without purchasing it again?

Would this work?

Thanks in advance...