You could hack it via the import session record in the data registry, but you'd need to know how to change it. I suppose you could take a DB backup before running the import step and restore that after running it.
I'm having trouble getting polls to import correctly (this is importing from MyBB 1.6).
The poll stage completes, but the poll results do not display as I would expect (i.e. they don't match as they would appear on the source forum). I have rebuilt the poll cache.
To clarify, for each discussion with a poll, the poll question seems to be correct, as do the possible answers, but the results themselves are not. When I say results, I mean the integers don't match the poll question.
I've run the poll stage multiple times with no success.
At this point, I should say my MyBB installation wasn't typical as such, but the database is entirely functional and the front-end of the source forum display polls correctly.
1.) I had to remove a duplicate poll entry from the "mybb_polls" table because two rows referred to just one thread. The imported continued without error after I did this.
2.) I had to modify the MyBb.php file to remove empty values because my database contained an extra delimiter on the end, resulting in an extra poll option (maybe this is where my problem lies, but maybe not)