That would be sweet, if it's not too complex to make it of course.
Anyway, found the starting positions. It turns out, it's quite finicky to change it. This will also work for Hot Pursuit, so you don't have to use the trick Zalcus20 wrote down.
00001860 (+4 for the next player)
In the base game, the value for first place is 07. For Player 1, this value is always 00, which means you'll always start last. But if you have 15 racers at the same time, you're gonna have to change the numbers for those extra drivers. Otherwise everyone will spawn at the same place as you, and that will cause the game to build a tower of cars. Police and traffic seems to ignore this address.
00001880 = 08
00001884 = 09
...
00001898 = 0ENote how I didn't add 0F on the address 0000189C. That's because the game doesn't know where to put the 16th car and will crash on the loading screen. So
15 racers at once is the limit. Also something that I need to add, when you return to the Race Results screen, the game doesn't have proper text for: 13th, 14th and 15th.
Now we need to tell the game how many AI drivers that's going to be participate in the race. This address is at
00001150. We're 15 drivers in total (-1 because humans doesn't count here), which means it's going to be 14 (0E).
I
did say it's quite finicky. If this value is too low, the cars will spawn at the starting line, forced to do an extra lap. If it's too high, the game will crash after you do 1 lap.
00001150 = Number of AI Drivers
00001154 = Number of AI Cops (Dunno if this actually change anything)
00001158 = Number of AI Traffic (Same thing here, maybe it helps the game to spawn them correctly?)
Something else I encountered, I manage to move the entire starting grid. So everyone started at the forest area in Celtic Ruins (around half a lap forward). I have no idea how I did it and didn't get a picture of it unfortunately.