Would it be possible to add an option to add materials from mods yourself with crafttweaker scripts oder in a config? So you wouldn't have to add everything on your own and mod compatibility would be increased a lot, I think.

I second this suggestion. A config file where you could manually add and tweak materials would be great. For example:

Heads = {{"[name]" ; [damage multiplier] ; [mining level] ; [durability multiplier] ; [enchantability] ; {(optional/mult)[item/oreDict material]} ; {(optional/mult)[built-in enchantments]} ; {(optional/mult)[built-in potion effects to user]} ; {(optional/mult)[built-in potion effects on hit]}},
{"Unobtainium" ; 2.3 ; 4 ; 3.2 ; 1 ; {unmodtainium:unobtainium_ingot} ; ; {minecraft:sharpness:1, minecraft:fortune:3, consecration:blessing:1} ; {minecraft:haste:2, minecraft:strength:1} ; {minecraft:weakness:2:5}},
{"Meteoric Iron" ; 1.5 ; 3 ; 2.4 ; 10 ; {unmodtainium:meteoric_iron_ingot, ingotMeteoricIron, ingotMeteor} ; {} ; {} ; {}}}

(if no unique texture is supplied, instead tries to auto-color generic tool part images with the material's given material item's palette, or if the material item isn't specified, the first matching oreDict material's palette. textures can be transferred from a server.)

HeadTextures = {"[associated name]","[associated config/toolbox_materials folder]" ;
"Unobtainium","unmodtainium_unobtainium" ; 
"Voidmetal","thaumcraft_voidmetal"}

config/toolbox_materials/unmodtainium_unobtainium:
pickhead.png, shovelhead.png, hoehead.png, macehead.png, etc.
config/toolbox_materials/generic_fallback:
(used for and recolored for Meteoric Iron and other unspecified materials since they doesn't have a unique texture folder specified)
pickhead.png, shovelhead.png, hoehead.png, macehead.png, etc.