I think you have a beef here, but I don't think you can make that type of rule change during the playoffs if there is no precedent.
In my one keeper league that I have been in 10 full seasons now, we lock the rosters once the playoffs start. You get hurt if your players are injured or don't play, but then again you can't pick up people to mess up other teams. I was really hurt this year in it having McCardell, Priest, and Blaylock all out and not having people to replace them with, but somehow made it through it. We had roster requirements by position so that made it more difficult. Didn't just have a bench of 5-6 players.
If you are still upset about it, I would suggest you recommend a rule change and put it to league vote for next year. That way something like this may never happen again if the league members agree that a change should be made.