It turned out to be relatively simple, but with an unanticipated glitch. Having made what I thought were all necessary changes, most of which simply involved altering
from django import newforms as forms
from django import forms
I tried accessing the site and got a lengthy traceback terminating in
ImproperlyConfigured: Error while importing URLconf 'urls': cannot import name newformsThis would have been fine, except that the traceback didn't actually give me any information about the module that was causing the problem. Ultimately I traced it to the registration add-on, which needed the same change making to it as did my own code.
I'm pretty impressed, even on a small site, that such large changes to the code needed such small changes to my application before it worked. Kudos for code quality to the Django developers. But it would be nice if the error message could be more informative.