Simulation / Emulation of an I2C EEPROM MEMORY (M24LC16B)
For an I2C eeprom you can manage with a micro controller acting as an I2C slave, just you need to process any messages quickly, as you do not control the clock, and most devices do not support slave clock stretching,

on top of this you will also need to handle what communication method your using to talk to the micro, remebering that this cannot interrupt the I2C handling, 

Other methods for on the fly modification of content is either FPGA to use internal memory, or 2 EEPROMS with the clock and data lines switched, so you can program 1 while the other is in use, then when the clock is idle for long enough you switch back over to the new programmed one.