How to use a library bundled in an AppImage

I’m looking at an AppImage for an application that has proven very difficult to build from source. But I don’t want to use the application itself, I want to use its libraries. So, here are a series of questions about doing this with AppImage.

Is there a way for one AppImage to include or be based on another AppImage?

Is there a way for something outside of an AppImage to link to libraries inside an AppImage?

Can I include extra files in the AppImage on the fly?
Can I change the command to run on the fly? yes
These last two questions are based on my experience with flatpak: With flatpak, I could use --filesystem to include a python script in the flatpak, and then --command to execute my script instead of the default binary. That script could then import the python libraries that are only distributed in the flatpak. Is there something similar with AppImage?