its not quite that easy.
you need the ofw.bat on the micro sd for booting ofw. and the cfw.dat on the micro sd for booting cfw. they need to be flashed to the ps3 every time you swap. this takes only couple seconds.
Not sure if they can be on the same card at the same time. but those are the files needed.
edit: search fast dual boot. no need for flashing its true dual boot not half dual. requires small mobo alteration fats its resistor removal , slims its trace cut.
slims fast dual boot is easy. fats lil tougher, going to make a tute for fats.