Hey there.
I have an industrial application that requires hard coded MAC addresses. I know a few years back most USB to ethernet adapters used EEProms but, many have switchd to One Time Programable chips to store the MAC address and USB identifiers. So my question is do any of your USB to 1GB Ethernet adapters still have an EEProm on them and are supported in Linux. I could then use ethtool to change the MAC.
Barring that does pluggable do custom orders where I could get a specific MAC set on like 50 adapters?