Workerids are unique, you can't register my registered workerid to your pool account. But you can mine for someone else's worker, which I think may be a huge problem now when the threads are limited, because someone could just kick out of the pool anyone not anonymous by simply mining with a few more threads on their workerid and cause them to go over the limit which will have them revert to solo mining.
This is why I just changed to anonymous and changed my workerids.
This is why I just changed to anonymous and changed my workerids.
All right, earlier I tried to see what would happen if I mined on someone else's workerid and the answer is nothing. It wouldn't kick them from the pool and it wouldn't even increase their hash rate, which is all good. You only get the connection refused error in the debug.log. So that also probably confirms my suspicion that it's not possible to mine with multiple computers on the same workerid (except probably dual CPUs on a motherboard on the same network connection), so the top users on the leaderboard are really using only one CPU for those high hash rates.