stars doesn't matter. I've said it many times, game programm players, with hidden % of effectiveness. That's why a 4* player can score more than a 8* player. The only mode to know if a player is good or not, is looking how is he playing, if he "do something" or simply don't.
In my experience I've seen that players are programmed in 1 way, and if they are effective, effective they will be (with a min. of, for example 5* in attacking skills, or something like this) I comproved it with Edgar Davids. ..well... and more guysxD

In the game as the mate say, the game never select the 11 names of players to appear, so, if you don't see a MC/ST name in 50' change it.
Too If a ST fail all, during 50' (shoot... 4,5,6,7 times and fail all) change this.
Is goog idea, that if you can do a change in the 75' put a ST too, will be fresh and if you study how work your substitutes, playing 15'-20' you can obtain something good.