I've actually done this, but it didn't work for some reason. No errors or anything, but my DC stayed Japanese region.
Also, fuck ISO's. I roll legit. I just have a mix of Japanese and US discs.
did one of the points have a resistor?
I also tried it, the guide says to feed a resistor 12v, it didn't matter which end of the resistor, on my Dreamcast there was no resistor at all, the 2 points where the resistor would have been solderrd to were there but no resistor present.
I had to get the 12v to the correct point or the region disc wouldn't do anything.
I finally got it to work, I can change regions now.