Edit: setting up Asset manager to work.
Here on how to use crate’s tool to extract .arz.
As for what you want to do, extracting the file and building all of them into .arz as a mod should work.
Another solution is to make a mod with only the files you want to change, since you have them already extracted. Make sure you maintain the same path to the files as the mod or it will not work.
1.Build your mod. Now you have an .arz for your mod, with the mod’s name.
2.Go to where that .arz got built and paste in the .arz from the mod you want to change. 3.Rename the .arz you pasted in to whatever you mod is called.
4.Build again. The files in the .arz got replaced with yours.
5.Restore the original name and past it back in from where you got it.