If you're seriously going to add this rule, then at least add it after Week 3 is completed. Adding a new rule in the middle of a tournament is... what the 10 people commented... Also, if you're going to call it "mid-week" substitution, then any manager could just substitute someone else in that match up if they don't like the match up. While anyone can just place one, two, even three "weak" battlers in DP OU and see how the match ups come out, then make substitutions. This can be used as an unfair strategy. Obviously, any manager could use this strategy to obtain some sort of advantage. In my opinion, the whole substitution method seems flawed.