Quoting Michael Paoli (Michael.Paoli@cal.berkeley.edu):
Not sure why I didn't think of it earlier (perhaps it wasn't quite as obvious earlier), but another approach which may be highly feasible ... use WWW::Mechanize to load options!
Probably practical. But please see unsolicited opinion, below.
But I notice list admin can't make *some* member changes (e.g. disallows list admin to change member's password ... at least one Mailman version I looked at)...
That's the major one. But it doesn't matter.
When I did a rush migration of the Skeptic mailing list from Johns Hopkins's Sympa instance (from which the list was being ejected because of no more university affiliation) to my Mailman instance, I just used the site admin command-line tools and ignored some of the fine points. I _did_ do separate adding-users runs for plaintext preferene vs MIME preference and for regular mode vs. digest mode, and then I told people 'Hey, you're here. Feel free to adjust your individual member options and make them the way you want, because I'm not guaranteeing them and you can fix it yourself.' That includes subscription password.
There was no point in working myself to death just to achieve utter perfection. And that includes no point further scripting it, either. IMO.
So, personally I wouldn't bother with the fine points on this migration, either. Go for the 80% that matters, punt on the 20% that's more difficult but also dirt-simple for each subscriber to adjust to suit.