Playing Hostel Cards

[JayRay]

I just played Munchkin for the first time at GenCon this past weekend and had a great time. As a result, I purchased the game and played a game with some friends right away. However, a question came up while playing that we weren't sure how to handle. Hopefully someone here can straighten it out.

One friend currently was level 8, went looking for trouble and brought out a monster he could easily defeat. He asked if we would be playing anything and we said we wouldn't since one point wouldn't let him win. We hadn't noticed, however that he had changed his class to Orc and, because he defeated the monster by more than 10 levels he would get a bonus point. Once he announced that two people wanted to play cards to buff the monster he was encountering, while the other two players thought that it was to late.

So my question from the above situation is, when new information is announced for the result of a fight can players react and play hostel cards to attempt to block the outcome?

I love the game and can't wait to play more, but I think this situation could come up a lot so I wanted to know the right way to handle it.