Returning to Belgium or moving to another country
When you either move back to Belgium or go to live in another country (for which a different embassy or consulate is responsible), it is definitely in your interest to inform your current embassy or consulate of your departure, preferably in writing.
If you so desire, the embassy or consulate can issue a registration certificate detailing your stay within its area of jurisdiction and mentioning your date of departure. When you return to Belgium your municipality will need this certificate to re-register you. In principle you must report to your municipal authorities within 8 working days of your arrival in Belgium.
Your data in the National Register will be updated by the relevant Belgian municipal authority (if you return to Belgium) or by the Belgian embassy or consulate with which you proceed to register (if you move on to another country).