Wasn’t sure what you meant but it seems merely hitting ‘save’ on the permalinks settings page without actually making any changes did it. I can’t thank you enough.
The point of two WordPress installs: I need two versions of the site which will be almost identical except for some specific differences in the (largely identical) content.
It’s clear to me now that I was in over my head and I should stick to editing the site with plugins and themes until I have a better understanding of how WP works. I’ll find someone else who knows what they’re doing to set up the second version.
Thanks again for your help.