Modding in a shield with 1.18.2 pre-existing minecraft code

So, I've been looking and looking at all of the ways that I could possibly mod in a custom shield into MCreator, however, I keep running into the same results over and over again. Either I use outdated 1.12 code made by one user on MCreator(https://mcreator.net/forum/51204/tutorial-how-make-shield), or I use a NorthWestTreesGaming tutorial(https://www.youtube.com/watch?v=1BPYnksQ8PI&t=1s) and make it faulty. So I have an idea(which is probably gonna be debunked very quickly), and this goes out to you code nerds(I'm very grateful to you all), would it be possible to take pre-existing code in Minecraft and use that to make a shield with it? Like, copy and paste it from Minecraft into MCreators code editor? If so, could you possibly teach me how?