-snip-
We're still waiting for 100 respondents. We have received only 47 reponses so far.
Is it possible to change the rules? Made in two parts, prizes are distributed after getting 50 participants and the other 50 participants will be distributed in the second round. In my opinion, if someone gets a prize, the enthusiasm of the other members will increase. That's just my opinion, but you have the right to use the rules you've created, waiting for 100 participants
It is possible if they wish and they have the right to decide whether to wait until they get 100 responses or change the rule.
Your suggestion is good so early participants do not need to wait for unknown/unlimited time till they get all 100 responses.
Its been more than a week but still less than half, maybe they need to consider to do your suggestion because it may take more week(s) to get all 100 responses.
Or maybe they can set a deadline, no matter how many responses they get on the deadline then they have to close it.