Blender Mod Character Rigging

I have a game-mod character that already includes its own mesh and original armature. Unfortunately the armature came into Blender in a completely disjointed state, so Rigify stays greyed-out and no standard rig can be attached. Because this mesh is hard-linked to existing .json and script files inside the mod, the model itself (geometry, bone names, hierarchy) must remain untouched—only the rigging layer may change.

What I need is a clean, custom rig built on top of the current structure so I can animate the character in Blender and send those keyframes back to the mod without breaking compatibility. No animation work is required right now; the sole deliverable is a fully functional, animator-friendly rig that respects the original bone ordering and transforms.

Please:

• Re-align or rebuild controls so the model deforms naturally in typical humanoid poses.
• Keep vertex weighting consistent with the existing mesh; no stray influences that could distort in-game.
• Provide the finished .blend file plus any helper scripts or add-ons you use, along with a brief note on the export steps I should follow to test the rig inside the game.

If you see a neat way to integrate IK/FK switches or other quality-of-life controls without compromising the mod pipeline, I’m happy to hear it, but the priority is simple reliability.

File, reference screenshots, and the current armature will be supplied as soon as we start.