When you download the custom races, they come with their own maps. Is there a way to play the custom races on other maps?
There’s no “add this race to the general map pool” option. It’s custom data unique to that map. You can open a blizzard melee map and copy all the data, imports, and triggers from the custom race map and then save the modified blizzard map as a copy to play it with the new units. Unless someone’s written a program to take custom data and assets from one map and inject it into the base game data, you will have to add the custom races to any map you want to play with them on.