Is it possible to add the ability to change tool efficiency levels?
And perhaps durability; but this is more for completion than need since that can also be done with crafttweaker.

Sorry, I won't do durability, which is out of scope for my mod.

And what do you mean with "tool efficiency levels"?

If you mean, that a tool is not necessary, but improves mining speed, you can already do this: https://github.com/tyra314/ToolProgression/wiki/Block-overwrite#effective-tools

np regarding durability. With efficiency I mean the speed at which a tool breaks a block. https://minecraft.gamepedia.com/Breaking#Speed

I may add this. No ETA tho.

In the meantime, there is Alfinivia, which should allow you to change the break speed.

ty. That is actually a pretty cool mod.