Indigenous Peoples Status Act Article 8

In the event of intermarriage between mountain and plains indigenous persons, individuals concerned may agree to alter their status to either mountain or plains indigenous persons to be the same; children of said marriage adopt the according status.In the event no status alteration agreement has been made, their children may acquire the mountain or plains indigenous status or alter such status through the arrangement of a statutory representative during the period the child is a minor, or by personal preference after the child has reached legal age.
中文原文 原住民身分法第8條
山地原住民與平地原住民結婚,得約定變更為相同之山地原住民或平地原住民身分;其子女之身分從之。
未依前項規定約定變更為相同之原住民身分者,其子女於未成年時,得由法定代理人協議或成年後依個人意願,取得山地原住民或平地原住民身分。

English translation for reference only; the Chinese text prevails. Not legal advice.