Bit of a premature post on my part here. After excavating the topics here, I found http://wordpress.org/support/topic/change-gamepress_video_category-slug?replies=4 the bit at the end:
Then just before the function ends with ‘}’ add another line:
flush_rewrite_rules();
Is what I was missing.
Hopefully this will at least help anyone else with similar issues.
Kudos to the dev for the sweet theme 😉
