The eng hboot 1.04 is required for aosp roms like cm9 and such, the alternative to aosp are sense based roms, which can also be flashed with the same hboot, minus few like venom (don't remember what type that was atm) and sense 4.0 roms I think which require the 1.57 or higher hboots, I ran mobsters on both hboots fine, while you would not be able to run cm9 on newer hboots, so yeah your able to switch then as you please just make sure what you flash after is compatible