Could you consider enabling players to change the personal mission selection when a tank is already in a battle?
This could be particularly useful because most missions need different tanks eg. lower tier tank for kills missions and higher tier tank for damage missions, but when a tank is already in a battle and destroyed, its not possible to select a different mission of the same class till the battle ends. I cant think any negative effects of it by which one can take any unfair advantage of missions by any way, coz the mission selected for a particular battle will be "tied" to the result of that particular tank which went to battle selecting it.