All metallic items can be melted down and turn into fluid.These melting recipes can't be removed or altered by config or CT scripts,making it impossible to disable a specific melting recipe.

That's already possible, you need to remove heating recipes by the recipe name. Each metal melting recipe is registered by [metal_name]_melting ie: bronze_melting.

But take in mind this will disable ALL melting recipes from said metal like ores, and also, your metal items will not be destroyed if heated above their melting point (which will make the tooltip - Liquid without it being liquid)