Convert NTG 5.5 Japan to Southeast Asia

[maximusmx]

Recently, I bought Comand NTG 5.5 to replace in my model. I bought a used one from Japan. There are two tasks that I would like to complete.

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

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