Override a File with Apache

I'm not sure (if and how) this can be done with Apache <directory> or .htaccess AllowOverride technique.

Scenario: two directories, a parent and child. The virtual host container for website points to
DocumentRoot  /parent/child
Within /parent/child is a default configuration file. Also, child is symbolically linked to another physical directory address; content is common distribution instance (Joomla) for multiple virtual hosts.

parent directory contains a custom configuration file. I want Apache to use or override to the custom configuration in the parent directory.

In IBM OS/400 world, this can be easily done with the override with database file command: something like . . .
OVRDBF FILE(child/config) TOFILE(parent/config)

Can this be accomplished within the scope of Apache?