Boot 2 roms... topic

I have read that it is possible to boot 2 roms at once? have searched around but the only thing i see if for the i9300 i believe and just curious if i can get it to work on my i747m so i can try another rom without having to get rid of mine and re-flash.... :S
Currently running Dirty Unicorns 8.1 and wanting to try slimkat and just figure it would be neat to be able to boot into either one without having to flash every time....

Any help would be appreciated!