For the record, I finally found a solution.
There is already a bash script in the rock pi s distribution that changes to a unique mac address. However for whatever reason this is not set up to run on the ethernet port, only on wifi. You can fix this by opening the file /etc/udev/rules.d/05-fixMACaddress.rules , adding this line:
KERNEL=="end0", ACTION=="add" RUN+="fixEtherAddr %k 06"
(Change end0 with eth0 on ubuntu version)
PS: Even this didn't seem to work on older armbian versions like v22, but on v24 debian build it worked.
