As of 26.05.2022 this mod is a vanilla feature in VRChat. This mod is not necessary anymore. THANK YOU KUNG!
Saves full body tracking calibration across avatar swaps in VRChat using MelonLoader. It works best with avatars that have very similar armatures. If the armature doesn't match and your calibration is broken, you'll have to calibrate just like without the mod. Now FBT Saver will save your calibration on a per-avatar basis. So if you've already calibrated into that avatar once, you don't have to do it again if the previous calibration won't match.
It also saves those avatar calibrations to your disk, so if your trackers are always in the same position, it will even save across VRChat sessions.