I didn’t know where to ask this question, so I’m putting it here. I’m playing with Ice and Fire and it overrides their copper and silver armor with the ones from here.

For 1.12, I would suggest CraftTweaker or some other method as the best way to remove the recipes. I'll need to check to see if I can make them conditional on copper/etc being enabled.

For 1.14 onwards, I would recommend using a datapack to null out the specific Mystical World recipe. Alternately, you can use an empty recipe replacement with a similar format, like

{
"type": "mysticalworld:empty"
}

which will simply result in the recipe doing nothing.