Certificate Custom Data

Hello I'm trying to print a date of when a user has passed a course on the certificate. Would you be able to let me know where I could hook into the workflow to alter the data that is getting sent to the PDF generation. Have tried a variety of hooks that I thought might work but with no joy, or is there something already built in that I could use. Have read through the certificate.module but I must be missing it. Thanks again for a great product, keep up the good work. Edit : Think I found a way, but if there is a cleaner way or an already built in functionality, please, do enlighten me : On nodeload : if($types[0] == 'certificate' && arg(0) == 'node' && arg(2) == 'certificate') { etc ... //Whatever the url is to the cert. ... $nodes[$nodeID]->body[LANGUAGE_NONE][0]['value'] = 'find a custom "token" that is in the template and alter it....'; //Alter Body/Html passed on.