TOPIC: Adding to the registration fields

I am creating a Spanish event. In Spain most people have a second surname, and also complicated addresses. I would like to add a number of fields to the "non-custom" registration fields, this is critical for the usability of the form and integrity of the data being collected.

I know that I can add a custom field for the second surname, etc, and also edit the labels, but this is not a solution for this problem.

I've started to look through the /components/com_dtregister/dtregister.php file. Please could anyone advise of all the places that I would need to add the code to add the required fields and also would I need to add fields to the DB for these extra fields?

Regards