Race-change limits
A person can change the race record twice: once before 21 and once at or after 21. A child can follow either parent or an acceptable mixed race; citizens may choose a double-barrelled record of both parents’ races. Siblings under 21 from the same parents should have the same record. The race-change application is free, but an IC holder must then update the IC and pay the applicable replacement fee.
Official ICA source
Written independently from ICA’s English original. The linked source supplies the complete document and subsequent updates.