Worked like a charm, thanks!
You can test this. Write down several old URL’s. Update permalink rule as desired.
Now navigate through site to see new permalinks, but also use the browser to enter these old URL’s – they will still work and you will see your new links!
This raises an important question, though. Even if the old URL will still function should someone click on a link to it from another website, wouldn’t that fiddle with the Google results? I wonder if Google will notice the new permalink URL of an older post, and simply write it off as duplicate content.
The only reason I even want to switch to permalinks is because my hosting stats program refuses to display individual posts in the “pages by view” category. I’m not even worried about how a URL displays, but rather getting AWstats to show many how many views each post gets.