Is there a way to change how many of a unit can be spawned in at once? Like how the max for special classes is 4. Is there any way for me to increase that?

In your mode's lua, look at the setup teams, the second number is the max

Well I want to make it so it is more than 4 in the regular game, not a mod map.

Without munging a new mission.lvl or hex editing, the answer is no. With a new mission.lvl or hex editing, then sure you can change almost anything (anything thats not done in ZE). However, some of the special units require extra memory pool stuff. If you increase the unit counts above the memory limits, the map should crash.

Ok I can hex edit, I just need to know what to look for.

Download and install the mod tools. Create a blank map, then follow computergeek's advice.

Tip: Munge a blank map, then change the value in the source and munge again. Hex edit the mission.lvls and see where/what changed. This should help show you where the shipped mission.lvl needs changed.