yeah mods change js components and easily modifiable things like damage values and other properties. Core engine components need to be compiled (c++ files) or depend on things that need to be compiled and therefore cannot be applied as a mod.
Once added to the main game, we could, however, modify the weight values and other things @atrik has set up in the unit templates. And that could be nice to test adjustments in the community mod.
I don't know what mods can possibly do (never dealt with them in any game). I assume you mean that they can't change the engine, and that's why this can't possibly be part of the community mod?
@Thalatta come on... The reason you had to build it to test it, it's because it changes the engine (like 90%+ of the change of this PR are engine improvements).
I don't know how things work exactly, but would have expected that at some point things like these would be added to the community mod (or whatever) for more people to test (since not many build), for then to go through review to be added to the next release? Or maybe I swapped the order of things in the middle.