Mac - Installing a Mod from .zip file

I would like to install some new countries, however the zip file is not exactly self-explanatory and also the one time I did try to do it myself I ended up having to overwrite the policies.csv file in the simulation folder, I know I did something wrong because the game would not launch after I attempted to install. Sorry in advance if this has already been answered, I searched several times to find the answer to my questions and failed.

Thank you in advance to anyone who helps.