As far as I can tell from my own uses of this, tools that have durability still have durability that works exactly the same as normal. I'd like to suggest a few changes regarding this:

• If the added tool breaks due to durability, revert to base morph-o-tool, instead of breaking the entire morph-o-tool
• Config option to allow certain named tools to not degrade in durability when attached to the morph-o-tool
• Support for mending/unbreakable enchants on the morph-o-tool itself, which applies to all attached tools that have durability