Please have alloys only be loaded if the material has an ingot supplied by another mod. For example, I have the ingredients to make bronze, but no mod I have installed uses it. So I have recipes for a molten liquid that I cannot use and a cauldron appearing in JEI that cannot be obtained. I request this as I am creating a modpack aimed to be as streamlined as possible, with zero content overlap and highly consistent and bug free.

A solution would be to detect what mods are loaded and if there isn't a molten metal registered yet for the metals in that particular mod, register it. It would involve code to support for each major mod though. The main ones I would think matter are Thermal Foundation, Immersive Engineering, Ender IO, Tinkers Construct, and Base Metals.

Something like:
if immersiveengineering is loaded
if molten nickel is not created
create molten nickel
if molten steel is not created
create molten steel

Yup, that's what I'm working on, but I've been busy the last week. It'll come.

Nice. No rush, just glad it's coming.

How about hiding these recipes in JEI?

Because I dont want my players accidentally creating an alloy they cannot use.

What I'm doing in my pack is just removing these recipes, but I've already mentioned wanting to PR in this exact change at some point. I'll have a look at it soon. IIRC, the issue is that at time of liquid creation, you don't have access to all registered items, so checking for existing ingots is not a possibility. The option to enable/disable metals in the config is possible though and I might do that.