If I do pool mining at difficulty=1000 and I find a share with difficulty=2000, I can tell the pool that I was mining at difficulty=2000 and then submit the share. I can earn more in this way.
Does the pool allow me to change difficulty whenever I want? If not, assume that it let me change difficulty every 30 minutes, then I can use a high difficulty which makes every share more than 30 minutes.
Even if this cannot be done, when I find a share with difficulty=2000, I can connect to the pool as a new worker with a static difficulty=2000 and submit the share.
What is preventing me from doing this?