Jack
Sorry, I did realise this would happen to a few people but there would never have been an ideal time to release it.
How would you like to be notified of such changes? What would grab your attention and ensure that you saw it in time? And how would you normally expect to receive information like this?
We could do app notifications, in-game mail, email etc. I want to implement a solution to ensure you're informed next time there's a change like this.
1) Show a stripe with important messages on top of home page as you were doing months ago. Nobody can bypass the home page by mistake.
2) Add the information on the league wall but please make the list longer (now you only show 1 message on mobile and 2 on browser which is too few).
3) Remember to communicate changes in advance unless you are fixing an exploit or a blocking error. The setup was not the case and you could have done it with 24 hours of notice.
4) If for any reason you must do it without notice, compensate what you are going to break. i.e. A perfect setup applied to any car racing next race for this change.
If you follow this rule of thumb, nobody will ever complain. Didn't you claim once that you would like to develop the esport side of game? So that's what you should do. Game rules and conditions should be clear in advance to deliver fair play.