M499 - EEPROM Invalidate Command

[Roberts_Clif]

M499 is not an officially supported GCode. If you add the code to your firmware it will work. But, you don't really need it to get your firmware's EEPROM updated. Its just a 'Nice to Have'.

Please Explain how this M499 works then so I can write it down.

[3Dave]

So, I've been looking at this trying to understand it - You edit Config.h with the specifics for your printer, you flash the printer, print something and turn off the printer. When you turn it on again the controller ignores the edited Config.h and restores the pre-flash values held in the Eeprom. Is this correct? If it is, do you need to add M500 to the end of the Config.h before you flash? And if M503 prints the settings from RAM, how do you print the settings from the Eeprom?
Sorry if I'm being a pain, but I really feel I need to understand this.