It's possible to update the caption of buttons and other controls in an ArcGIS Pro add-in. It should be possible to do the same for groups. I can get the group object using FrameworkApplication.GetPlugInWrapper method, but that returns a not-updatable object (NoUpdateWrapper). The reason is to be able to change the control captions on-the-fly. I have created my own language combo box in an add-in, where the user can change the current language on-the-fly.
