What if the chip is an 8K EEPROM that took the place of some other EEPROM. SO the Plant is just to cut a trace with a tiny drill then solder your memory in place of an existing memory chip. That is not very complex just a simple swap.
It is very common now to use memory with a serial or "I2C interface because it uses very few PCB traces. Having few traces make the swap simple
Here is an 8K EEPROM that you can order today
http://ww1.microchip.com/downloads/en/DeviceDoc/21710K.pdf
it costs 25 cents for one unit.
Look at the SIZE. if you order the "CS" package the chip in less than 1 millimeter square. A grain of rice might be larger.
These chips are use on many designs for critical things like a boot loader or who knows.
I can find other chips that do different things here is one slightly more complex (with more pins) that is still 2 x 3 millimeters and cost 31 cents. buy it here:
https://www.digikey.com/product-det...ology/24LC02BT-I-MC/24LC02BT-I-MCCT-ND/857624
But that said here is my #1 pick because I know it is dead-easy to use and has a great support ecosystem...
Look at the "Tiny4" AVR processor. It has a CPU, RAM, ROM and I/O divices and is about 3 millimeter long and cost well under $1. This is an entire computer on a small chip and you can buy them retail. I've used these and keep some in a parts drawer. They hold a lot of C++ code and can do some complex things. If you have a yellow wood pencil this chip will fit on the eraser. read more about them here:
http://ww1.microchip.com/downloads/en/DeviceDoc/ATtiny4-5-9-10-Data-Sheet-DS40002060A.pdf
If I was going the plant a device this Tiny4 wold be my "go to" unit.