WordPress is the most popular software to build websites. Therefore a huge choice of experts is specialized on customizing plugins and themes.
We recommend you start browsing developers and web designers at Fivver.
Your developer should make sure that
- you will be able to update the plugin without losing the changes; and
- additional code will not throw errors when Tag Groups is temporarily deactivated (e.g. during updates or testing).
See also the resources for developers.