As far as I know, the only way to specify the order of drop-down menu commands on a piece is to pay attention to the trait order. This can be mitigated by using Triggers.
Sub-Menu will present its sub-commands in the order listed. If a sub-menu is not named, the commands do not appear at all.
This gives rise to an idea: that if a sub-menu is not named, the sub-commands should appear in the piece’s top level menu in the order listed in the unnamed sub-menu trait.
Alternatively, the request could be satisfied by a new trait.