[koz1000]

I was working on an 8-bit system back in this same time period. We couldn't afford flash devices and the kit required to reprogram them. But we did a similar trick with an extra write pin located near the ROM socket, then used a special daughterboard filled with SRAM that replaced the ROM and also touched the write line. Now we could just use our cheap debugger and blow an image into the address space the ROM used.

Only downside was that you lost the image on power down, so I can see why EEPROM was more important to Apple in developing their systems.