On birth certificate, it modifies the transgender law of 2018 (ANSA). In Belgium, people with a fluid gender identity will be able to change sex on the birth certificate several times in their lives.
Or change your name without changing sex, or take a name regardless of gender identity. This is provided for in a government bill that will be presented tomorrow to the Justice Committee. The bill did not fully resolve this issue, stating a possible "stigmatizing effect" from the introduction of an additional 'X' category.