Doesnt flashing with custom firmware debrand the phone already?
Yea but id of thought you'd root first, and use the recovery to make a nand backup, and then apply your custom rom, and even custom roms come with crap you dont want, and you still need root access to remove that.
I always flash an original firmware, then the rooted PDA, then use recovery to apply my custom rom, in that order, just makes sense to me i guess, clean install from the start, ive had issues with trying to slap one custom rom over the top of another before.