In most cases, there's no need for one rule per URL.
If the URL structure has been properly designed, then a small number of patterns can be used, each matching hundreds or even thousands of URLs and programatically redirecting to the correct new format.
If that's not an option, then use a redirect script that captures all of the requests for old URLs, looks up the new URL in a table, or database, and then issues the appropriate redirect HEADER data back to the browser.
Many thanks for your help. I am semi-competent with Dreamweaver but I am not up to writing scripts, unfortunately. All I really need is a 'before' and 'after' sitemap with differences shown, preferably also with 301 redirects inserted. Dreamweaver may be able to do this (maybe I should ask on that forum) by saving the current sitemap, saving the new (modified) sitemap and comparing the two files to show differences. All the differences would need editing but at least it should be better than doing the whole thing manually. I may be able to do the same thing with the XML sitemap generator. But I feel sure there must be a utility somewhere to automatically generate the 301 redirects.