I was just looking at my page for playing imports on a Sega Saturn and figured I should fill some people in on how to change country codes on Sega CD games.
Right now, you best bet is to use SCDConv (download). This utility can convert most (not all) Sega CD ISO images to a different country code. This is handy if you have an US Sega CD, but a Japanese game, you can run this tool on it to convert the bootcode to US, so it will play on your Sega CD without additional carts or modifications.
Here’s how to use it:
in a MS-DOS prompt, type “scdconv
Here’s a compatibility list for SCDConv, so you can see some of the games that work or fail with SCDConv. Please submit failed or successful conversions to Eidolon via email, so we can keep this list updated!