Ah, sweet, that should make things easier.
In terms of passwords, what will probably happen is I post a message on the login page explaining what happened. Particularly if someone tries to log in with a pre-flarum account. At the very least, I don't want people to go through a lost password form without knowing why their correct password isn't working.
I could blast out a mass email to all members when it goes live, just to let them know. Undecided on that though, don't want to be spammy or anything.
In any case, I'd have to do it myself because that script looks like it only creates the SQL to run in your Flarum database. Shouldn't be too big of a deal though.