Thanks, Justin. I tried it – I simply changed my permalink setting from ‘post name’ to ‘default’. I then refreshed a browser window that had a long, ‘friendly’ post name – it took me to my home page (not the page I’d been viewing).
So my experiment tells me that changing the permalink setting away from ‘default’ is not to be done lightly, for if one does so, they will have to stay with their choice to ensure that all old links (especially from other sites) will continue to work.