No 7C81 board found

Well its tricky because you need to disrupt the user
image load but not subsequent the fallback load.

Don't have the data sheet in front of me but it's the
SOP8 W25W16 or W25Q32 chip

"Another option is to make a EPP cable fro the 7C81
and reflash the card via EPP (needs a PC with a EPP
capable parallel port running Linux and a funny cable)"

Can you give me details on this procedure?
By the way, thanks for all your help.

You would need an adapter cable like this:

 

The run mesaflash from a PC with EPP port and
reflash the card with the desired SPI firmware

Thank you PCW. Now I have three approaches to fix my mistake. I'll report back on which ways I try and my results.
Much better than mailing it back with the shipping charges being half the price of a new card.

A related question: what does the 7c81epp.bit file configure the board to do?

Its a 5abobx3 configuration but with a EPP interface

So you could configure linuxcnc to use an EPP port with a 7c81 , without requiring a RaspberryPi? Wow, that's what I call versitile!