Its an older game so it's coded for a hardware spec that is far below what todays machines have.
There is no way to increase the number of ents it can hold without modifying the code.
However, I have created a utility that allows you to keep a stash of zipped mods in a folder and install/remove them at will with very little effort.
you can find it on my site
click "Downloads" and pick "Treadmarks - Tools" from the drop down at the top of the downloads page.
the file name is "TMMMInstall.msi" the TM Mod Manager.
It uses .Net 2.0