Hello icryptic,
Please download the child theme of SuperMagPro and install and activate it. If you need to customize single page, just put the single.php on the root directory and customize it. If you need to edit others file, just make the same folder structure as parent theme and only add the files you need to edit.
http://www.acmethemes.com/blog/wp-content/uploads/2016/04/supermagpro-child.zip
If any problem arise, let us know.
Best Regards,
Acme Supports