No.
No prefix. That is the entire point.
The current URL to the pages are
www.example.com/page1.html. I need THAT EXACT URL to be maintained with XF installed on the site, otherwise all the old links break.
I would like to "upgrade" the links to improve the appearance by removing the file extension, but that's it.
I have shared this exact information repeatedly, and explained in great detail. No prefix.