@fritoss007 I can give you a hackers approach at doing what you want with the registration process. FOG calls fog.man.reg to invoke the registration process. You can find the source of this program here: https://github.com/FOGProject/fos/blob/master/Buildroot/board/FOG/FOS/rootfs_overlay/bin/fog.man.reg
If you understand bash shell programming you can make modifications to this program to alter it registration. I will give you a hint to use notepad++ to edit this file because windows notepad add extra windows junk into the file that will cause error messages during execution.
So now you have this file how can you inject it into the FOS Linux booting process?You can do the recommended method to unpack and repack the inits as Sebastian outlined. Take a bit of the hacker approach and use a FOG pre-startup script (i.e. post init script) to copy the fog.man.reg from the FOG server to the FOS Linux disk as FOS Linux boots. If you look at this tutorial: https://forums.fogproject.org/topic/14278/creating-custom-hostname-default-for-fog-man-reg in the section called fog.patch.customhostname you can see how to “patch” FOS Linux as it boots.