creating custom initrd

[info at boer-software-en-webservices.nl]

Is it possible to define which modules mkinitrd should add to the initrd?

I have a custom initrd, but after every kernel upgrade, it recreates the
initrd. When it does this,
I loose the extra module I need, so I end up recreating the initrd
myself again.

I know in Ubuntu and Debian there is a file somewhere in /etc/sysconfig
that defines the modules
to use when building the initrd. But I have yet to find this file in Fedora.