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 Codeable or 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.