The author begins by discussing their previous speculation about the possibility of programmable Mac ROM SIMMs in Quadras. They suspected that developers at Apple during the 68k Mac era could reflash the ROM in their Macs, similar to BIOS updates on PCs. Multiple people pointed out to the author that an Apple internal utility used for ROM flashing had been uploaded to the Macintosh Garden. The author ran the utility on their LC 475 and was able to dump their existing ROM and verify it. They then disassembled the utility to understand how it works and discovered a table of entries for compatible ROMs. The author also discusses their experiments with creating a compatible SIMM and using the utility to flash a new ROM image. Throughout the content, the author shares their experience and provides technical details about the process.
https://www.downtowndougbrown.com/2023/11/how-apples-developers-reflashed-mac-roms-in-the-90s/