Yes. I have done that very thing on two different sites.
I have a PHP, MySQL / DataAssist created Admin page that I created to perform the management function. Add, Edit, Update that kind of thing.
I have a Button that physically WRITES (fwrite) the XML file output that I hand coded to meet the XML requirements.
All in all it works very well. Once the new file is written the Flash file will instantly recognize the changes the next time that page is opened.