I posted in template forum originaly but didn't get any response so thought maybe I should try. Hopefuly this helps someone or gives a possible idea to developers.
I tried to use
Director::addRules(80, array( 'sitesettingsmodule/sitesettings.css' => 'SiteSettingsCSS', ));
in _config.php but received a 404 page not found error.
I was doing this to create a css page so that I can have a dynamic CSS page which I can control from the CMS. For example being able to change the background color from within the CMS.
i have used this method before to create XML pages, no tag pages, php pages and all to no problem. I had a look in the back end and couldn't see any where this was blocked. Anyone had any experience with this? it seens like it could be a bug, I don't see any security reasons as to why Silverstripe would block it but perhaps they didn't think to include it either.
Thanks very much for your help.