Forking gradle dependencies on Android
I say just make a local module which depends on the other library and modify that. Don't forget to record which changes you've made. Ideally, you import the module as a separate commit in the VCS, and then you modify it in another commit.
This has the advantage that if you want to update the library, it will be fairly easy to do since all you have to do is copy over the source for the new version and then make the same modifications. However, if you take the other approach, then you'd also have to push all the changes to GitHub, which adds complexity, but little benefit unless you want to share your modifications with someone else.
This seems like an unusual circumstance - Maybe an example would help
Also consider composition before resorting to forking libraries.https://en.wikipedia.org/wiki/Composition_over_inheritance
class YourAdapter { private AdapterA adapterA private AdapterB adapterB}