It sounds like you may be interested in potentially making a mod (or you are just interested in someone else making one, in which case the following resources should be helpful to such a person). You will probably need to learn C#, PowerShell, shell, etc. and work with this SDK:

https://github.com/OpenRA/OpenRAModSDK

You can look at community mods here to find examples to learn from and see what is possible:

https://www.moddb.com/games/openra/mods

You can click on one of the mods and potentially find their own git repository, such as this one: OpenE2140

This mod used Lua as well: Generals Alpha

To prove my point that you can make a mod with your own story and atmosphere, this mod is a (literal) bug swarm strategy game: OpenSA

For the mod itself, you will be mostly programming in C# and sometimes another language if you decide to use one (it seems with this particular engine, modders tend to either use just C# or C# and Lua). Shell, make, and other languages are typically used for the packaging and installation/generation/compilation/etc. scripts/tools of the mod.