You have a crowded model with many things in it.You have created several groups using CTRL+G.You want to modify one of the groups.The way to do it at the moment is to drop the group (drop element tool), make your changes and then regroup the elements using CTRL+G.
A better way to do that would be like in some graphic design software like Illustrator for example:
You double-click the group you want to modify.The group is isolated, but the other elements are still visible, but you cannot catch them accidentially. Similar to the behaviour when you "activate" a reference file.You make your changes to the group.Afterwards you can go out of the isolation mode somehow. Right-click --> End group isolation ... or something similar to that, would be an example.Another way would be a double click outside of an element to go back to normal mode.

Why I would like to have such a feature:In my company we are planning industrial plants and we have several vessels, reactors and so on. Each of them is a group (created using CTRL+G). If we want to change anything we have to ungroup and then do a regroup afterwards. When regrouping you have to watch carefully to not get any of the other parts into the group by mistake, or you have to move the group to the outside where it stands alone, ungroup there, regroup there and then move it back. These steps and the time could be saved with the way described above.