it doesn't seem that tricky.... just give me a link
OK, if you think so....http://arakon.hn.org/
Just so you know, it is tricky and here's why.
It's a bios swap. Yes, you can solder the new bios on top of the old one, but that only works well at all for the original Sega CD model 1 (stacking type) since you cannot solder the backside of a model 2 due to it's placement. If it looks like it's just a couple switches in my picture, it's not. I had to remove the original bios CAREFULLY since the traces are microscopic and easily screwed up, and then solder in a socket.
I know what I'm doing and I screwed up 2 and a half Sega CD units doing this mod. Yes, "half" since I was able to partially recover one of them. And one of the ones I did is currently giving me fits of unreliability (though I think the fix is simple, just need to open'er up and try it out).
You can get a feel for how difficult the mod is by reading the web page above by the guy who designed it, a very good modder. He also fouled up a couple of these systems doing this mod.