Hi, I'm literally brand new to modding, wondering where to start?

I’ve been watching the Salcarr’s modding tutorials and they’re super helpful. I want to crate a new recipe now, but I’m not exactly sure how I can apply it to existing recipes. Like metal walls. I want to change the requirement to metal, and a new item, but I don’t know how I would be able to apply it to all of the metal engrams, like walls, ceilings, and the like. Would I have to duplicate the existing engrams and change it from there? Or can I just change them in their existing folder without having to copy them?