It's not quite the same as back then they were EPROM's and not EEPROM's or flash. So you'd have to actually pull the chips out, erase them with a UV Lamp and then programming then in a Burner.
It's a long story but after I left high school in New Jersey I had entrusted a friend Mark to ship my possession to California where I had moved to. Instead it stole it all.
After moving I started a large collection of BIOS for XT, AT 80286 motherboards. I had written code that was floating around the BBS's that would harvest the BIOS and dump out ROM images that you could burn on to EPROM and install in to another Motherboard.
So I had made several sets of the latest AMI bios for some friends back home. Well Mark asked a mutual friend to get a copy of the BIOS from me, but not tell me who it was really for.
Well I found out and prepared a special BIOS just for him.
Mark was a big warez guy. He was sharing floppies with everyone.
So I took a copy of the Friday the 13th virus. Also know as Jerusalem B that would slow your PC down to a crawl and every time you ran a program it's file size would grow. It was very easy to detect and clean and mostly harmless. I removed the malicious payload , but made sure it still propagated normally.
The virus was only around 2000 bytes, and ran as a TSR.
I found some empty space in the ROM image, and xor encrypted it and placed it in and added hooks so when you format a floppy (Int 13) it would install the virus TSR.
From there it would then attach itself to any exe file that get's ran.
So I burned the EPROM's and sent them over. I was hearing story's from friends how he was loosing his mind. He'd clean all his disks. Then go to make someone a copy and it would be infected. No one would trade disk with him.
He never did figure out how he kept getting infected.
Revenge is sweet.