X-Decor-libre is mostly self-contained but it allows for limited extension with a simple API. Not that extensibility is not the main goal of this mod.
The function documentation can be found in the respective source code files under the header "--[[ API FUNCTIONS ]]".
These are the features:
You can register tools to be able to be enchanted at the enchanting table.
See src/enchanting.lua for details.
You can add a custom hammer for repairing tools at the workbench, using custom stats.
See src/workbench.lua for details.
You can register "cut" node variants of an existing node which can be created at the workbench. This will add thin stairs, half stairs, panels, microcubes, etc.
THIS FEATURE IS EXPERIMENTAL!
See src/workbench.lua for details.