One possible "harmful" aspect of thread creators changing/deleting the options in a poll is to skew the results in a particular way.
We try to stress that the Poll feature is for entertainment value only, though many people take them seriously.
As mentioned above, the staff will be happy to alter a poll for you if you report it. We can also reset the votes, or delete a poll entirely, in which case you can create a completely new poll for the thread.