What it says on the tin. Polls should be editable. This is particularly important so that someone (e.g. third-party scruntineer) can add the GPG key after the election administrator has created the poll.
We can use the same interface that we use for creating polls, just pre-filled with the info from the poll. When you save, it just overwrites the old poll config with the new one rather than creating a new poll.
For the MVP, polls should not be editable while they are in the voting stage. At that point, if you've still messed the poll up it should just be aborted/cancelled.