Yes, the hypervisor on the MEGA65 already lets you have 10 different ROMs, and pick which to load by holding 0 through 9 down on poweron. This loads MEGA65X.ROM from the SD card instead of MEGA65.ROM.

You can also just make a program that loads in a ROM from a disk image, asks the hypervisor to disable write-protect on the ROM area, copies it back in, asks for write-protect to be restored, and then jumps to the reset vector.

Paul.