The main issue you will run into with decompiling is that it obfuscates things by losing local variable names, slot names, custom flags, comments, etc. The more complicated the mod is, the more difficult it will be to integrate Diplomacy and whatever other systems you wanted.
If you are familiar with the Module System, this will be a pretty difficult task.
I am partially familiar with the module system and I have found a way to decompile the hole mod now. The big issue however is that I have truly hit a very big wall.
The source file for Diplomacy isn't like freelancer where each section of the mod is independent and modular. Diplomacy is the whole damn module itself which complicates the development massively.
Right now, I see only three ways to avoid this issue.
The first issue is splicing each of the Diplomacy files into The Last Age .py files, this can be extremely painstaking and will most likely result in a lot of crashes or errors because I forgot to set one line of code in the wrong section or botched it during copy/pasting.
The other way is quiet literally reverse engineering Diplomacy with The Last Age's models, items, troops, banner and troops.
Super daunting task that will most likely take a year which was not my intention at all, this was just a spruce up from the original mod to make it more stable.
The first option is more attractive, otherwise, I may as well make my own mod with diplomacy.