So I'm feeling pretty stupid.
I downloaded a mod that came with its own mandatory resource.cgf (mandatory as in the creator said you need the resource.cgf file that comes with the mod in your mod folder) but I already have a resource.cfg file in my Mods folder that came with the base game.
What should I do so that I can have both? I can't have two files in the same place with the same name. I tried putting the mod and its resource file in a folder - that didn't work.

Can anyone help?

I'm not positive this will work, but I think I remember seeing it... Try taking out the original resource.cfg file (from the base game) and use the one that the mod needs.

Make sure you save the original resource.cfg somewhere safe in case you need it. You prob wouldn't want to reinstall everything if it didn't work out.

What reason did the modder specify for needing a new Resource.cfg file? The only reason where using an edited version from the one originally provided is to have more embedded folders. That's to have a folder, within a folder, within a folder, so the game knows how many levels deep to read them.

The original version only goes two or three folders deep.

If a modder made it so folder A holds a package file, that goes inside folder B with another package file, that goes inside folder C with yet more package files, that all goes inside folder D with even more package files... then you start to see the need for an edited Resource.cfg. Like Russian dolls within dolls. That's all the Resource.cfg does. Tells the game how deep to read folders within other folders; subfolders. Nothing more. If its needed for a mod, then that is what the mod is doing, folders within folders more than the standard issue. Though now I'm baffled as to why a modder would even do that?

How old is the mod? Because when TS4 was first released, "script mods" (Not Package mods) could not be read by the game if inside of folders. Maxis patched that yonks ago so that script mods could be read inside a folder. But only one folder deep. Put a script mod into a folder, then put inside another folder, then the game cannot read it. What I'm guessing here is the mod in question may be older than the Maxis patch where script mods could never be read while inside a folder.

Lastly, the modder may have actually created a new Resource.cfg with an "Overrides" folder setup, so that while in the main mods folder it overrides anything that could potentially conflict with it. When you place this mod into your main mods folder, is it held with an "Overrides" folder? The Overrides functionality does not come with the standard Resource.cfg.