Can I add policy groups and modify the credit rating system?

So I’ve been snooping the forums for a bit and came up with an idea for a mod. However, since it has a fair amount of new policies and simulations planned, I feel that lumping them into another category (such as ECONOMY) doesn’t feel right or accurate.

The mod itself revolves around Monetary Policy and its effects on the economy and voters, so I feel a whole new policy group should be added. What I found, though, was that in order for my changes to take effect, I actually had to change the strings.ini and policygroups.csv in the Democracy 3/data folder. If I tried to make duplicates of those files and place them in my mod’s folder (Democracy 3/Monetary Mod/data/…), they wouldn’t take effect. Is there something I’m doing wrong or can I simply not do that?

Also, I’d like to add an option for the credit rating system by which other countries won’t lend to you anymore, given a certain condition(s). Would that be possible as well, or is the credit rating mechanic hard-coded into the game?