When answering a CNR challenge it's common to get the response: "Well done, but that was definitely not what I had in mind".
I feel like it should be perfectly fine for anyone to post a second crack if OP says the intended solution was substantially different. The first crack is of course still valid, but the challenge could still be a very interesting to others, since they know there are other, possibly more complicated, complex or obscure solutions.
I've never seen anyone posting a second crack, and OP often posts "The intended solution was:
abcde. (I've done this myself quite a few times).
Can we encourage others to post a second crack to the cop post if there is a substantially different solution to it? This would also mean that Cops are discouraged to post the intended solution until the SAFE-date, even if it's already cracked.