I knew I recognized the filename... couldn't think from where.
It's called hacking any time you change core code for an extension. Unfortunately, I can't tell you how to do it either way, but it's usually possible to accomplish something without hacking.
Hacking is bad because, although it might solve a primary goal, usually it affects other processes that will cause problems. It's best to hire someone to do it properly if you aren't sure how yourself. This coming from someone that's still hoping to learn coding herself someday in the near future.
The only problem with hiring someone to do it, is that the plugin may or may not work with upgrades, and since Groupjive is not finalized, it's very possible the whole framework will change before the stable release. So you may need to update your job as the plugin evolves.