Good stuff man. Great N64 collection!
Have you tried rubbing it with a q-tip or paper towel dabbed in rubbing alcohol? Most permanent markers should come off with some rubbing alcohol. Just keep it away from the label.
The dry erase method may work but the surface of N64 carts are coarse, so just trying to wipe it off without some kind of solution would probably leave some leftover ink.
What ever you do, do NOT use a Mr Clean Magic Eraser, since that's basically microscopic sandpaper and will remove the finish on the cartridge.
No, I haven't tried yet. I've been organizing my stuff and figured since I now have access to people who know what they're doing when cleaning old games id ask before potentially screwing up my games
(I still regret writing on them with a sharpie when I was little D: , but in my defense I did it because I was made to lend someone them and I didn't trust th to try and not keep my stuff)
Thanks all for the advice, I'm not sure when I'll get around to cleaning them, but I'll be sure to let you all know how my endeavor turns out :0