you can leave the chip there, just cut the vss,vdd and chipselect lines to the CoB
Umm, wouldn't you then have a unpowered ROM chip sitting on the live data and address buses, loading it down as the bus powers the ROM through the I/O protection diodes? I like the CS cut (I'd also add a pullup on the ROM side of the cut).
then place a flash chip on top and solder the legs to the correct address lines
Oh, this I really like. Especially if the ROM and flash devices have a similar pinout, so that you don't need much blue wire. Great--OKI shows a cross to an AMD Am29DL640D flash device! Hopefully mine has a TSOP ROM, so that I can just swap it for flash...I wonder if they brought out the write enable line to the ROM footprint...
additionally you can use a flatpack flash chip and "dead roach" it to the ram chip
Hmmm. That would get you the data bus, power, and about half of the address lines. The pinouts look pretty different; pile o' blue wire?