Currently there is no command in TBASIC that allows it to set ID. We figure that it is not very safe if a program is able to modify its own ID which can cause trouble to a network of devices that are connected via RS485.
The ID is stored in an EEPROM address which is not accessible by the SAVE_EEP command. These are meant to protect the integrity of the system.
We have added this as part of the "wish list" features for future development.