Ok, being very precise;
On CosmoKramer's RB custom it saves to my NTSC save, since it's an NTSC game.
On the PAL GH2 Custom I have, it creates a new PAL save file, saving only to that, since my GH3 and Wii are NTSC.
Therefore I made a new career mode to play the RB custom and not affect my GH3...