Thanks for the quick reply!
For now it would be totally sufficient to have one fixed IP for the boot image to be able to boot one at a time. This still would make it possible to create multiple different USB-Boot images with different IPs as long as it is only a small number of bootimages that one needs. So that should be way easier as the following.
If it would be possible to have something like a complete list / mac to IP mapping on the bootimage, one would need to create that list.
How to assign IP while boot?
Using a created udev-script or systemd-networkd.
I was thinking of using systemd-networkd and create the config files for each mac:
.link files for physical devices = name deviced from mac-address
.network files = match name = the one created from mac-address
Where to store the information for the list?
In the central computer imformation, where we already have stored the mac address.
There could be additional fields that allows to store a fixed IP address (+ gateway, Subnetmask ...) if one wants to create a bootimage with fixed IP addresses.
Then one could mark every computer that he wants to create a single bootimage for or simplier make a bootimage and create a list from all computers that have this information stored.