Combatmode seems to be picked up by what the leader is set to...
General Barron's right, it's definately a group property. However it's not taken on the group as a whole (as you might expect it to be
).
I noticed while writing a platoon command engine that detecting combatmode for a player led squad would only return what the player's combatmode is.
If you set the player's combatmode (via a script or trigger) to another mode, then it will return correctly. You'll also notice the red square next to the player's unit (if set to hold fire), which you won't be able to get rid of unless you use another combatmode change via a script/trigger.
Anyway, bottom line: I don't think the player can change their own combatmode in game... only that of their group. The
combatmode command will return the player's combatmode, not that of the group as a whole.