I looked, that jump table doesn't have any unused entries.

There only seems to be one function that writes the menu value, BTW, so if you wanted to pull up a menu on demand you'd probably just call that. Also, I checked out the values the game actually writes. All that really showed is that 5 is used whenever you enter an area in Adventure mode. I also found that if you actually have it write 0 (title screen) instead of 1A (first screen), instead of simply swapping the pointer, you get a perfect intro skip directly to the title screen, so I might just have to look into finding where it gets that 1A and changing it.
Also, 810E836A 16D4 skips the memory card/rumble pak warning screen thing, but the Game Select menu will be broken; the menu doesn't show up, and you can only press A to select Tracks mode. If you only want to play Tracks mode, though, then it works fine.

(You can of course go back from the track select menu to get to the proper game select, but that takes longer than going through the warning screen. <_<)
I'm thinking this "menu modifier" value may also be used elsewhere (possibly the same value stored in multiple places), or the "title screen" routine actually checks other things to see what to do, which would explain all the unused entries. I didn't see it write any of those values though.
[edit] I finally got a chance to test on the real system, and the intro skipper just seems to crash the game, but it hardly starts up without the GS so who knows if that's the code's fault or not.

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