It seems something change on Tinkers end with registering repair materials, thus now that ModTweaker can not remove or add repair materials as it throwing a null pointer while trying to apply the changes.

Error:
java java.lang.NoSuchMethodException: tconstruct.library.crafting.PatternBuilder$ItemKey.<init>(net.minecraft.item.ItemStack, int, int, java.lang.String)

I can paste a full log if you want but this is the main error being displayed.

Versions:

• Tinkers: 1.8.2a
• Mod Tweaker: 0.6-0 (joshiejack version)
  • I checked the source code for Tinkers; from this version and its the same as joshie's

Jared asked you for a log and the script. If you don't give it, we can't help you.
Oh, and if you do /mt reload Modtweaker commands do not work. You have to restart the game to use the command. Hopefully it is a bug @jaredlll08 can fix soon.

I need the full log, and the script you are using.

I did some more testing and managed to get it to work for Vanilla items/block only but the /minetweaker materials seems to not be working, so I can not get the modded added materials to add metals to be used for repairing.

The error being displayed:
No such minetweaker command available

Going back the original bug it works fine but for standard vanilla blocks/items. I would test with modded items but I can't find a way of me getting a list of the materials added as the command does not work.

Please look at http://minecraft.curseforge.com/mc-mods/228458-jsonables
It does exactly what you want.