You can edit a Group clip the same way as a regular animation clip in the Time Editor. When you create a Group clip you can still modify the clips inside it, then close the Group clip again and have these changes be reflected without having to recreate the Group clip.
Because you can add timing operators (such as Time Warp and Speed Curve) to a Group clip without affecting the timing of the clips contained within it, there are times when you will want to make edits to the individual clips contained inside. You do not need to remove the clips from the Group clip to edit them, you can create a Local Time Tab for them. See Create Local Time Tabs for Group clips.
To unpack a Group clip, right-click it and select Ungroup from the Time Editor Clip contextual menu and drag it onto another track.