Define/Insert key memo
List window: Click Openings, Theme, Strategy, Tactics or Endgame
If you decide that you want to move a key up or down in your list, right-click on the key you want to move. A popup menu will appear; select "Define key memo" in this menu (or press Ctrl-M). You've just told ChessBase that this is the key you want to move. Click once on the key that appears immediately above the position where you want the moving key to appear. Right-click on it and select "Insert key memo" from the popup menu (or press Shift-Insert). ChessBase will then move the first key to the new spot on the list. Once in a while, particularly when you try moving a key to the very top or bottom of a list, ChessBase will insert it above the key you've highlighted, so it may take a bit of tweaking on your part to get the list just right -- but it's certainly "doable".
You cannot use these functions to move an entry from one database key to another. Use transfer key to do that. But you can use Define and Insert key memo to move a subkey up or down in the list.