If you're going to do it, definitely change the jumper. Note: I'm not an EEPROM specialist and Rainbow has said that for some devices the programming voltage needs to be present on boot - maybe this is just when updating ESCD, I don't know. So I would change the jumper to 5v with the power off but if your friend's machine then fails to boot, change it back to 12v and set it to 5v once you've removed his BIOS ROM.