Making a mounted ISO image of a CD-ROM writable

[Paul Hoffman]

Greetings again. I want to make an ISO image of the FreeBSD 
distribution with a boot.config file that contains "/boot/loader -h". 
I have the ISO image as a file on my hard drive, and have mounted it 
on /mnt:

mdconfig -a -t vnode -f /path/to/my/bootable.iso -u 0
mount -w -t cd9660 /dev/md0 /mnt

However, when I try to create files on /mnt, I get:

-su: boot.config: Read-only file system

How do I make it so that I can write into /mnt so that I can then 
later save those back to the ISO image?

--Paul Hoffman