So I'm still hitting a wall in regards to getting the whole LAN process fully automated, but I've discovered some interesting extra stuff.
In multiplayer, setting the values for the course greater than the normal bounds allows access to some courses/course patterns not normally accessible in that mode. Mind you they aren't particularly useful, as they typically crash at the end, but it's just more stuff to play with. No, there aren't any new courses, but stuff like the sunset/night courses are playable.
Similarly, altering the sound number beyond the normal limits allows you to use background tracks not normally available. The end song, the menu song, even "seeeega" looping over and over are all options.
I need to see if there are corresponding values for the other game modes. If so this might be the key to properly adding new songs and new courses.