When importing the updated avatar, you can uncheck the FBX and any texture folders/files if you don't want those updated, so your edited model and textures aren't overwritten. Basically, uncheck anything you want to keep from your current version.

Since the fixes are mainly related to toggles/animations, you can usually update the relevant FX controller, menus, parameters, etc. without replacing your edited model or textures. Just be careful about overwriting any files you've personally edited.

If the updated toggles don't work correctly after importing, you can also fix them manually by putting the updated FX controller into the Animator and checking the Animation/Animator setup to see what changed.

As always, make a backup of your project before importing the update. That's how I usually work around these things in Unity, but the exact steps can depend on how the avatar creator packaged the update. And it works for most things avatar related too. Hope this helps!