[DiapDealer]

That Python file is strictly for the plugin framework. It has nothing to do with how the Sigil binary finds libsigilgumbo. You want to focus on the bash launch script for Sigil. There's cmake options (compile time) and environment variables (runtime) that can be used to relocate Sigil's various components. They're all documented in the Linux build documentation.

The short answer is that you can't just move stuff wherever you want. And you won't be able to move anything without using the provided script to launch Sigil. Directly executing the Sigil binary will get you nowhere.

The launch script is designed to look for libsigilgumbo in the same directory as the Sigil binary. Adjust the launch script and/or $LD_LIBRARY_PATH (if such a thing exists on Haiku) if you wish to change it.

Just note that changing these things could break some third-party plugin functionality if not done thoughtfully.