class_core.php and child themes

Zarko has kindly helped me with some additional code for class_core.php to resolve a category selection problem I’m having (when someone selects a sub-cat during the listing creation process the system also select the parent cat and flags it as an errow to them although everything still works….weird…) .

Is it possible to have a child class_core.php file / some way of implementing this in a child theme such that I don’t need to re-enter this code in the main class_core.php file every time there is an upgrade?

Thanks

Richard