Import/Export is definitely going to save time, not just one time, but every time some users need to be updated. Also, editing on the csv file is going to be easier. Just my suggestions. Convenience may be percieved differently from one to another.
Coming to the solution, if you would like to export all Groups and not just OOTB (out-of-the-box) groups, you may have to look at the MessageConfiguration table and ensure that the EventSource parameter for the export event is configured to match all the AdapterSources of the Group objects. Or you could simply make it to EventSource = "%:%"
If you would still prefer to edit via the UI, as per your original question, and if you would like to see more/different fields in the search pop window such as the Email Address, Supervisor etc., you just have to customize the appropriate aml Group (for the grouping of fields) . e.g. in your case, it may be EM_AssignGroupManagerDisplayUsers and then use a custom ChooserGroup on User object and that would contain custom fields like the Email Address.
Hope this helps.
-Shashi