I got a feature in the works, allowing to select and manipulate only "focused" items, which should hopefully be useful for manipulating grouped items without having to disband the group. There's a demo video here:
https://www.darkradiant.net/images/videos/selection_focus.mp4
It works like this:
You select some items in the map. It doesn't matter what it is, it can be a group or many groups or just two unrelated brushes.
Hit Ctrl-F to enter focus mode (the command is called "ToggleSelectionFocus" if you want to bind your own shortcut)
Your actions will be restricted to just that selection
You cannot select other items that are not in the group (unless you use Layer or Filter selections, or Invert selection)
You'll get a visual indication about the focused items in the ortho view
Grouping information is ignored while in focus, you can select single parts of any group
You can select, move, rotate, delete, edit vertices etc.
Hit Ctrl-F again to exit, or (maybe more intuitively) hit ESC until you left the focus
The previous selection (before entering focus) is now active again, you can proceed manipulating that
I'd appreciate if you folks could have a go and try it and then give feedback about it. There's no release yet, but you can grab a portable release from Github: https://github.com/codereader/DarkRadiant/actions/runs/3403010325