To create your own custom cover sheet, simply use your favourite word processor to make a document.
Make sure that the words 'machylafaxfrom', 'machylafaxto', 'machylafaxdate', 'machylafaxsubject' and 'machylafaxcomments' appear in the text
somewhere.
Once you are done, save your document in Rich Text Format (RTF). In MacHylafax, go to your preferences and click 'Cover Pages'. Click '+' and select your RTF file.