It might still be possible to spoof the MAC address to defeat MAC ACL - just more difficult. The MAC address on the older ethernet NICs used to be a PROM in a socket - yes, you could swap the PROM from one NIC to another - and is now probably stored somewhere in flash memory.

In theory, you could change the MAC by flashing the card, in similar fashion to flashing the firmware.

There are some sharp guys on the forum that have been flashing one manufacturer's card with another manufacturer's firmware, and reportedly even flashing from silver (64bit WEP) to gold (128bit WEP) - maybe one of them can figure it out