I could have sworn this was already in the mod, but I can't seem to find it in the configs.
It would be nice to be able to change the text on tools that displays their current level "Clumsy, Legendary, etc."

For example, if I wanted to add a tier called "Crude" before the others, or rename "Comfortable" to "Groovy."

They're configurable through resource packs - look at the lang files for the mod, and create a resource pack using the unlocalized names.