How do I build a custom installer?

Hello,

I have installed NetBSD/macppc on my Mac using the netbsd ISO. I can
boot off the cd using ofwboot.xcf and "netbsd".

However, I'd like to modify the "netbsd" kernel options.

I've successfully modified regular kernels just fine.

However, I've not been able to figure out how to do this for the installer.

To make my installer kernel, I lightly modified GENERIC_MD and built it.

When I boot, the system boots normally at first, then complains "no
file system for md0".

I noticed that the ISO installer file includes /bin, /etc, /sbin, and
several other files that aren't a kernel. ( I presume this is on the
memory disk, but not sure how it gets there, or if it's part of the
kernel build somehow ...)

What's the process for making a custom kernel for the installer?

Thanks