The procedure was pretty easy, I followed a PDF on gamefaqs. It involved opening up the Genesis, taking off the RF shield, cutting down into the board in one area, then soldering some wires to a single pole, double throw (SPDT) switch. I also had to wire one wire straight to another point, permenantly setting the console to 60 hz (I didn't bother rigging a 50/60 hz switch, as my TV can't handle 50 hz and the only PAL game I might import won't run right if you switch it back to 60 hz after booting it). Then I drilled a hole, enlarged it a bit, ran the switch down there, drilled two holes for the screws, and screwed the screws down through a very small o-ring (to give them something to resist, so they hold in tighter).
It works fine, though I haven't recieved the game yet. Booting Sonic 2 in Japanese mode makes Tails name become Miles. Some games give an error when booting up in Japanese also. Good stuff.
You can see I didn't do a pretty job, but it functions great.
One other little trick I had to do involved the cartridge slot. Japanese Megadrive games are shaped differently on the front, so I pulled out the old dremel and buzzed it down a bit to get my only Japanese mega drive game, Herzog Zwei (which is a great game, if you haven't tried it), to fit. Good times.
Anyone who is thinking about importing Japanese megadrive games and has a Genesis 1, I definetly suggest giving this a try. It was very easy and fun to do.
Guess that's about all I have to say. Yay.
mines better its made by X-net modz ill post pics soon theyre not on x-net yet