For the forth race thing, maybe a simple work-around could just be...
1) Make the forth race be all new units inside another race (just add new units and rename them and treat them as if they where another race)
2) Of caurse then the race isn't selectable so, you have to make the base building have a "morph" feature to change it into the base buidling (command cneter type thing) of the new race.
3) to make it symetrical you can just give each starting base no abilities and they all have to morph into which race you want (so if you pick terran then you start with a command center, and your 4 scvs. your command center and your scvs are dummy versions so they have no abilities except... they can morph into real command center, real hatchery, real nexus, (by real I mean the one you create as an aditional building but it has the real ablities of the origonal starting base of each race instead of being dummy) or the forth building, and then your fake scvs are destroyed and reaplaced with the real miners of that race.
Hopefully this all works like I think it does, and with it you can create an infinate number of races (limited by the limit of new units you can create of caruse, but still there are thousands of those)...
edit
and someone pointed out to me that those things in SCMDraft where you type in the ID (like 2008 gets you some weird unit, and all the way up into the high thousands all have (usualy useless) units) aren't really units (I still don't understand how they are there and have their own atributes but aren't really units), but I have to use all the stuff I can get into in scmdraft which still gives you enough room to do 4 units with this system, but it also takes up spells (which I also thought where unlimited) so it's still doable, but you can't make too many units, and you can't have too many spells for the new race cause every new one takes away one from another race. (unless there are some unused spells somewhere (doubt it)).
edit...
ok so you can get the ASM code of starcraft, which from there I guess you can find and copy paste code for a unused sc unit over and over (changing it's id each time) and doing the same for a spell? then you can edit those spells and change them around in a more readable program.
I know I should start with something simplier, but this has just got me curious =P, and I do know some basic assembler, I took a break from learning it a few days ago to try out smoething new and am now getting into modding as that something new....and now I need to learn some assembler to do modding, how ironic =P.