"upgrade the firmware to accept more RAM" and said that they had a 2ghz MacBook that they had done this to and all was well with Yosemite….I'm intrigued, can you upgrade firmware on a mac ?
Are you sure you understood them correctly ? Maybe they were just saying you could open it up and put more RAM in there ?
You can't just magically flash a computer motherboard (mac or PC) to accept more RAM ... the amount of RAM supported will depend on a combination of CPU, motherboard and operating system constraints....so its not just limited to some arbitrary number picked out of a hat by the manufacturer, its determined by system engineering constraints.
Yes you can upgrade firmware on a Mac, and Apple have in the past released such upgrades for various reasons ranging from Bluetooth issues to sleep problems.... but
AFAIK there have never been any updates that magically increase the RAM because that's simply not possible in system engineering terms.