I have used the process here- https://www.novell.com/support/kb/doc.php?id=7009943 to create my network install ISOs. But when I used it to make a SLES 12 mini cd all I got was garbled text when booted. I searched a bit and found a process that I used to model this proceedure.
I have an Install source on a server with the IP address of 10.1.6.128. The ISOs for the various versions of SLES that I use are saved there (/srv/www/htdocs/repo). I am going to use the SLES 12 x86_64 DVD iso as an example. It is located at /srv/www/htdocs/repo/SLE-12-Server-DVD-x86_64-GM-DVD1.iso.
I have mounted the ISOs via /etc/fstab with this entry:
Let's start by mounting the ISO and copying the files from the DVD to your local storage. My DVD is already mounted as an install source on my web server. You may need to manually mount it somewhere else.
When you have your new ISO working properly, remove the ISO source files:
rm -r /tmp/minicd
This process also works for adding files to the install ISO. Copy the entire contents of the ISO to the /tmp/minicd. Modify your source files to your liking. Use the same mkisofs command to create the new ISO.