Ah... Starcraft. It's 200 supply per player (hero units take 0 supply, zerglings are 0.5, and the supply cost goes up to 8 for battlecruisers for example). The limit is enforced when building a unit from a building. Map triggers can grant units and you can exceed the 200 supply limit.
The technical unit limit for the map was 1700, and was later in fact extended to 3400 by Blizzard. The EUD emulator (part of the official SC Remastered) allows for online custom games to be played without any third party tools on the player's part. Certain limits like sprites can be bypassed with this tool (for map makers) https://github.com/phu54321/euddraft/blob/master/plugins/unl...
EUD started out as a buffer overflow exploit which allowed custom maps to patch the game client's code. It was later fixed by blizzard but re-implemented as an emulator (with some restrictions).
These are definitely things that enhance gameplay for custom scenarios. https://youtu.be/HEv_U9WV4PA?t=1541 (yes, that is a battlecruiser shooting nukes)