To: Thane
You had that line included in 
http://wiki.tinycorelinux.com/Integrating+Extensionsunder  Section 2.
It's something to do with the mkisofs command.
Here is my script.  I've run mkisofs with and w/o a preceding sudo.
I followed the "Integrating-Extensions" link when creating this script.
# Install-iso.sh
# From: 
http://wiki.tinycorelinux.com/Integrating+Extensions#
# 1. Copy TC files
#
# 1.1. Unpacking from ISO
        # Copy iso image to /tmp folder
        sudo cp /mnt/hda1/home/john/Downloads/tinycore_3.0alpha8.iso /tmp/tinycore.iso
# 2. Add extensions
        tce-load -wi opera.tcz
        tce-load -wi nano.tcz
        tce-load -wi xfe.tce
        # Copy extension folder
        sudo cp /tmp/tce/optional /tmp/newiso/
        # Make necessary folders
        sudo mkdir /mnt/tmp
        sudo mkdir -p /tmp/newiso/tce
        # Mount and copy boot
        sudo mount /tmp/tinycore.iso /mnt/tmp -o loop,ro
        sudo cp -a /mnt/tmp/boot /tmp/newiso
        sudo umount /mnt/tmp        
        # Load other necessary extensions not to be 
        # included in the new ISO image
        #
        # Load mkisofs-tools
        tce-load -wi mkisofs-tools.tcz
        # Load brasero cd-burner
        tce-load -wi brasero.tcz
        # Load isomaster
        tce-load -wi isomaster.tcz
# 3. Create the ISO
        cd /tmp
        sudo mkisofs -l -J -V TC-custom -no-emul-boot -boot-load-size 4 
        -boot-info-table -b boot/isolinux/isolinux.bin -c boot/isolinuxboot.cat -o TC-remastered.iso newiso
        sudo rm -rf newiso
It should work, but it does'nt
Run it and see
Thanks
newbean