I have them set in the config to the following:
I:"Potion ID: Cinder Coat"=81
I:"Potion ID: Dissolve"=82
I:"Potion ID: Knockback Resistance"=83

And yet when the game loads, they are 33, 34, and 37 respectively, despite 37 already being used by Witchery, and the WG one takes precedence. I know this is an unsupported mod for an ancient MC version, but I just wanted it documented somewhere for others to see, and for the microscopic chance you're still doing anything with this mod.

IDs 0-32 are used by vanilla and Thaumcraft 4 (TC4's are hardcoded)