How do I make a default override to work uniforms?

Not sure about a proper tutorial but the way to do it is to find the Police Uniform CAS Part and remove the associated uniform tag on it so the game doesn't recognize it as such. (Make sure you selected Override.) Afterward, add that same tag to the CAS item you made so the game recognizes your CC as the uniform. It's also recommended to also have one swatch tagged as uniform if you don't wanna end up having mismatched uniforms like the Doctor Career. This isn't retroactive though so if you have a sim that already has a generated work outfit, they will not have your new CC as uniform. You need to promote then demote them again, or remove and rejoin the career to regenerate a new uniform. Hope this helps!