Since it's been continuing to bother me thoughout this afternoon, I have some further thoughts to share.
I've actually found this very demoralizing. I was very pleased with my score before this, knowing that it was a good - or maybe even very good - score for the previous ruleset but not an unbeatable one. And now everyone has a whole week to figure out how I did it & probably do better (especially with an extra freebie and no basketcase). I'm probably not going get any time for Sims this next week and even if I do, there the fishing event to do.
So after reflecting a bit, here is my opinion with regards to situations like this. Do with it what you like but I really hope you will keep it in mind if a similar such situation comes up in the future.
I think if you realise a challenge isn't working out so well half way through, then changing things for the participants at the last minute is still not a good idea. I think that it'd be a better idea to just let it end up being whatever it is even if that means it's a challenge that isn't as well balanced as usual, or one that ends up having lower participation or more DNFs than usual. (You can always chalk it up as a learning experience, one that may end up helping to make future events better). Personally l think that last minute rule changes are a worse option for this kind of situation & more likely to put people off.
This is just my opinion and other players may feel differently about it of course, but I'd be surprised if I'm the only person here who may end up less keen to participate in future if there's a chance that the things could be changed around on us at the last minute as they were this time.