FT_PROG is a free EEPROM programming utility for use with FTDI devices. It is used for modifying EEPROM contents that store the FTDI device descriptors to customize designs.
Warning! When you change the default FTDI VID and PID descriptors, matching against the original, FTDI drivers will not work anymore! Which means that any subsequent attempt to use FT_Prog with the serial to USB converter will not work! You cannot revert back the changes because the device is not longer discovered by the drivers.