Workflow for imported .glb with custom animations and tracks?

I'm trying to figure out the workflow to use for importing gltf and glb files with animations. For example, a Mixamo character with a handful of animations combined in Blender, then exported as a .glb file.

I have not yet found a workflow that can do all of these things:

1. add tracks to animations
2. add new animations (like "RESET")
3. integrate updates that happen when the .glb is replaced

I've been able to achieve 1 & 2 via "make local" on the scene, but at that point everything is local and detached from the imported stuff, so 3 doesn't work.

I've also been able to achieve 1 via the "save to file" and "keep custom tracks" advanced import options on the .glb itself, but then the RESET track disappears

I can only achieve 3 when I don't "mess with" the import, or when I create a new inherited scene. But the inherited scene animationplayer isn't writable... I can't edit or add animations.

What am I missing here? What is the workflow you're supposed to use for importing 3D assets with animations, then adding a RESET track, and adding sounds etc in the animationplayer, without "locking" everything to the version of the asset you used on day 1?