thats what i meant. i have done it for 5-6 times and only once the team playing proper formation for 80 minutes won (you need about 10 min to change both formations) . please take notice that not only i changed formation to illegal but i changed also the players positions (striker for goalkeeper, goalkeeper for striker etc). i used it playing against my wifes team and i had to use my reserves against her first team in order the 2 teams to be equal quality. if the 2 teams have a significant quality difference then you can't be sure about your conclusions since the strong team even playing illegal can win the weak.