When you make new multiplayer mission and place lets say 24 player slots there, its nasty to click them all through and make them “playable”, also when you merge or copy paste units they don't come with playable status set. So how to make all units quickly playable?
Open mission.sqm in text editor and replace string:
player="PLAY CDG"; skill=
And then load & save your mission in the ArmA 2 mission editor so it again formats mission.sqm nicely.
BUG: that adds it also to gamelogics, but you can fix it simply by double clicking gamelogic and pressing OK, then it removes it. I'm sure it adds it to many other objects/vehicles too… so maybe choose better solution ;)