There was someone looking to do something similar on romhacking.net the other day that had a bit more, though no nice addresses I can give you to look at.
http://www.romhacking.net/forum/index.php?topic=3282.msg391415#msg391415
Neither are the sort of thing I would particularly suggest someone coming in brand new to hacking to attempt*, however they are both within the scope of what a game does, reasonable for an earlier stage assembly project and if it is the thing that sees you learn hacking then so be it.
*you can mess with game functions but generally you would be pointed towards text, graphics and the like to get a feel for how formats work. Making cheats can also be a way in, especially for manipulating a game's functions, and while I would not bet against a simple cheat being possible for some of this I would also not bet on it.
8th place not being needed to finish was likely added more to prevent trolls and disconnects from messing things up for people. It could be a simple enough thing where you change a number but it could also be much deeper
Speed wise. If there is a mode that has everybody race as they would then see if you can fake that. Sometimes 150CC or mirror mode has this and it might not just be that but a flag the game sets differently. The link above mentions that the first two CPU characters will always race at full speed, and that . If I was programming it would either set a handicap to those later in the grid (they way C coding works means that would be fairly easy to pull off) or it would be in the coding itself to always have things. If it is just a handicap you can possibly do it with cheats, if it is in the code then try to find the CPU locations/information and speeds and see what is manipulating that number in a debugging editor.
