Convert NTG 5.5 Japan to Southeast Asia

[maximusmx]

I recently bought a COMAND NTG 5.5 to replace my model. I bought it used in Japan. There are two tasks I would like to accomplish.

1. Convert HU from Japan to Thailand.
2. Convert the map of Japan to the map of Southeast Asia.

Do I need to flash the firmware? Will my HERMES model work with a Thai SIM card without converting the HU firmware?