Guys, genesis isn't starcraft.
I'm personally not sure you could even do a starcraft mod. Not in any truly satisfying way at least. If you wait until curses are out, depending on what all options there are, you may be able to make a fairly satisfying zerg race. See if you can make buildings kill all the grass around them. Make curses that only apply to a single species(the larva) and transform them. Make buildings that produce items with specific curses on them and have your drones carry those items over to the larva, feed them, and transform them into your other species.
That's if you have zerg playable, and if you're making a starcraft mod and not planning on having all three races playable, then you're being cheap. What? Are you gonna release 3 packs each focused on a different race? (I'm really not even sure if that's sarcasm or not, you can have a single playable race if you want, it'd be way easier).
Zerg are the easiest to do, especially if curses have the functionality I expect, because they're all organic so you don't have to worry about things like vehicles. For other races though, vehicles are a serious concern. You could wait until there are mounts, but I doubt that will even solve the problem. One option is to just have vehicles be creatures with pilots in them, as another thread mentioned. This kind of works in starcraft because vehicles are trained as units, but there's no way you can just spawn... oh. Actually, if you can create curse-transformation items(I really hope you can) then you probably could make an item that is used in a reaction to make a cursed item that immediately transforms the person who makes it into a vehicle-creature. I really hope that becomes possible.
Ok... I had more, but I'm just too excited about potential curse-modding right now to think about starcraft.