No, you don't have to do that to all the tanks, just one.. right click and disable auto equipment, select the tank, add the equipment manually - if it tells you the equipment needed is on another tank then go to that one and manually demount it and come back.. once your tank has the equipment it needs do a battle then when finished right-click and re-enable.
Thinking about it all this *could* be because for some reason it was having a problem demounting one piece of equipment from that other tank?
Anyway, as I said hopefully WOT will add this function to the game themselves not least because we don't want to be charged to demount numerous times if our sub runs out.