Yep. When you flash a new ROM it flashes the kernel that is included with the ROM as well. Unless you are on the newer HBOOT where you have to flash the boot.img separately, then your old kernel should still be there. If it were me, I'd flash a ROM and then the stock kernel included with the ROM through fastboot, if needed. Make sure everything is running well and then go back and flash Rohan's kernel after that.