The file defines paths and callbacks, e.g.:
<access_arguments>access CiviMail subscribe/unsubscribe pages</access_arguments>
However, changing values in the file doesn't seem to produce any result. I changed the page callback above to CRM_Mailing_Page_Optout but the content served was again coming from CRM_Mailing_Form_Optout.
So how can I make any changes to the callbacks?