Well, while the ExtraTiC config doesn't have a 'disable this liquid' option, it does have options for altering ratios for making the alloys. What happens if you set the gold and iron input and the angmallen output all to 0 ingots?
As for using Modtweaker to remove the alloying recipe to make angmallen, try the following:
Code:
mods.tconstruct.Smeltery.removeAlloy(<liquid:angmellen.molten>);
The liquid id may be wrong, but you can check that yourself ingame with the "/mt liquids" command.