The EEPROM on the HAT can be updated as follows. Before the update the WP jumper next to the EEPROM has to be closed.
Install EEPROM utils:
$ git clone --depth=1 https://github.com/raspberrypi/hats
$ cd hats/eepromutils
$ make
$ chmod +x eepflash.sh
Generate EEPROM data:
$ wget https://github.com/watterott/RPi-UNO-HAT/raw/master/software/rpi-uno-hat.txt
$ ./eepmake rpi-uno-hat.txt rpi-uno-hat.eep
Update/Flash EEPROM:
$ sudo ./eepflash.sh -w -t=24c32 -f=rpi-uno-hat.eep
Note: For a Device Tree Kernel add to /boot/config.txt
the following line before flashing: dtparam=i2c0=on
(before any dtoverlay statement).