How to change functions.php using child theme

Hi, I’m creating a child theme of an existing theme, and trying to change the behavior of functions.php. Specifically, I want to change the directory of some files which is in require_once() of functions.php.

If I simply put my require_once statement in child’s functions.php, PHP claims conflict in function names and WP doesn’t work.

Acctualy, the final thing I want to do is to replace functions in the files located in the theme’s subdirectory. Does anyone know any simple way to do this? Thanks a lot in advance.

I’m new to this forum and have posted a few questions so far, but I’ve never got a reply…