The problem with hand editing the file is that Glade is very picky and this might make the next change made with Glade have irrelevant changes as it adjusts your hand edits. Perhaps wait until after #2860 and then you can use a modern Glade instead of having to hand edit or compile Glade 3.8.5.
As for moving the menu, we don't want the top level menus getting too large, that prevents use on some small screen systems. But `Edit` isn't the longest menu, so I personally don't care if one more top level is added, but depends on what others think.
You will also have to sort out the mnemonics, `s` is already used in the top level edit menu.