How to update Linux YUM repo in Guest OS During pre-boot

I have an Oracle Linux 8 VirtualBox guest that gets configured with Vagrant. During the build yum packages need to be installed, but from my disconnected yum mirror instead of the Internet facing yum servers.

I want to know how to replace the /etc/yum.repos.d/OL8.repo file that’s in the guest with a file that instead points to different yum repos so that my package installs will work properly.

I’m new to Vagrant, so your guidance is much appreciated.