rel="category tag"

I have one last vaildation issue still on posts related to this lengthy post and discussion re: rel=”category tag”

I tried to copy the function to my child theme’s functions.php file and edit rel=”category tag” to rel=”tag” as applicable (and noted in the linked to post), but received an error message…do I need to create my own function or how does one override a function from core (and not a theme)?

I did edit the core file wp-includes/category-template.php to test and the homepages do now validate to HTML5, but I would prefer not to edit core files….any thoughts?

[ Please do not bump, that’s not permitted here. ]