I am currently working with Alexbunny over on the FFXI Modding discord on a workflow to import meshes into the game, either via Blender or other sources. It's not quite polished enough to share yet, but it will be really nice when it is!
Also, the 'all races' portion was done via a python script which searches for hex signatures and modifies the data directly rather than other tooling. I'll have it up on my github later this week.
If I remember correctly, it was always possible to change meshes, but the game would freak out if you didn't have the exact same number of vertices as the original. Have you figured out a way around that, or is it still a major constraint?
(Imagine being able to make whole new models for everything, and not just modify the existing ones; one step closer to FFXI remake in FFXI!)