@redkittens - In general, you should not be modifying the module javascript files. newsfeed.js, clock.js, etc work pretty well and you just need to modify your config.js to configure the modules correctly.
For example, you’re trying to modify the newsfeeds that are used by the newsfeed module, yes? Any configuration that you put in the config.js will override the defaults in the newsfeed.js module. You don’t need to overwrite the default values because the Magic Mirror framework will do it for you.
If you need to add functionality to a module, then it’s a different story. But in my experience about 85% of what users need can be handled with careful editing of the config.js file.