I've got a XML page www.example.com/page, but my server results it as being text/plain because it does not have extension.

So I wish to add XML Header via .htaccess to any or all the files which does not have extension with a disorder that the file is available. As though file does not exist, program is performed from database also it decides what header to output, so I'd rather not break that part by intentionally altering header.

Give a DefaultType text/xml (or whatever type you are using for the XML) for your .htaccess.

Other command place the inside your .htaccess (however it will pressure all files to possess the information-type):

ForceType text/xml

http://httpd.apache.org/docs/1.3/mod/mod_mime.html#forcetype