Revert .package files help!!!!

@Disfigures I know you're looking for TS4 help, but one point made by posters here is relevant to you. Your computer opens the files in notepad because it "learned" to use notepad by default the first time you tried to open one (when you were likely prompted to select an application for the task). Without intervention, it will continue to attempt to use notepad by default for every file of this same type it encounters. You can remove this association using the steps listed on page 1, but it's not strictly necessary. As long as you're not trying to save the files after you open them, you're not actually changing them, and the game itself doesn't care which application your computer thinks it should use to open the files. It should be reading the mod as it's supposed to regardless.

I don't play TS4, but with the release of the new game pack (and likely a patch as well), you may be having compatibility issues with mccc. The mod's website should tell you if you'll need a newer version, which may or may not be available right away.

There are several threads here devoted to help specifically with TS4's mccc where you can post about your issue. Here's one:

https://forums.thesims.com/en_US/discussion/913483/mc-command-center-local-help-chat-thread/p57