>>367809521
if you just overwrite the FBX in your assets, you won't have to redo any materials or rigs. the only exception is if you change the armature, you may have to reset and re-enforce the T-pose in the humanoid rig config.

also if you do ANYTHING, make sure you do not "break the prefab instance" or "unpack the prefab". You will lose the ability to change something in Blender and then re-export it to Unity if you do that.