I see this is about GT5U so I cant help 100% with it, but there is no way to MineTweak that stuff the way you want it. GregTech is designed to always make sure equal things are as compatible as possible, configuring your Modpack to make things incompatible is basically impossible to pull off, without doing some serious source edits to GT5U.
GregTech doesnt just grab it during launch time, it grabs it the instant moment something is registered, you cannot put anything inbetween to intercept it without changing the GT Code itself to make an exception for the Pams Salt.
Also it is Salt of all things, the stuff that should be abundant in Oceans. Why nerf that?