No, that's what I was referring to when I spoke of coding into the engine "universal player abilities". In Glest, all actions that effect units are processed as a skill (or series of skills) in a unit's XML and combined with a command - also in the unit's XML. Without a unit selected, Glest has no XML (and thus no skills and commands) to display to the player.
The only power the player has is to move the view, select units, and then issue any commands currently available to that (or those) unit(s). You can no more issue an "attack" without a unit (and one with an attack command at that!) than you could run a computer without a motherboard or CPU.
Yes, changes would be required and I don't know how much those changes would require.