1. No, sometimes I conceded a goal after the substitution but also I can score one after the sub - usually the sub is involved in either. While I'm waiting for a substitution to complete I often get a possession drop but we've not had a goal in that dip so far this Season.
2. Yes, a little, but I expect that, normal. I have 4 MCs, 80 matches between them for 8 yellows; 5 defenders, 99 matches for 7 yellows.
(Imo a lot of the poor MC ratings come from fouls (as well as playing a role/tactic their not equipped for) - its the engine room.)
3. Ofc its possible that you can concede a goal while changing formation - there is usually a reason why you're changing it.