zorro:
is there a way to do an internal mod?
Yes, but you better be prepared for some work.
Over at the Turbo Mailing list, they house <a href="http://joyce.eng.yale.edu/~bt/turbo/files/country.switch" target="_blank">THESE</a> instructions on doing an internal mod. Basically you are rerouting 8 data lines to swap between TG16 and PCE mode.
This only works on US machines to the best of my knowledge. There are some other mods required if you want to covert a PCE to TG16 mode. This is because even with this mod, an actual PCE still not play a TG16 game. I believe a pin on one of the chips inside has to be wired to ground from 5 volts. <a href="http://joyce.eng.yale.edu/~bt/turbo/files/pce.hardware.mod" target="_blank">This</a> document goes into more details about this.
I would also just suggest getting a JP machine instead of doing these mods. That is unless you can pick up a Kisado adapter for a stoopid cheap price (which most likely WILL NOT happen).