Registration inoperative for trusts approved or notified under exemption provisions; opting for section 12AB cancels prior exemption approval. The amendment expands the registration references to include section 12AA and section 12AB and inserts two provisos: (1) registration shall become inoperative when a trust or institution is approved under the exemption clause or notified under the relevant notification clause, or when the proviso comes into force, whichever is later; and (2) a trust whose registration becomes inoperative may apply to make registration operative under section 12AB, but doing so will terminate the earlier approval or notification and the trust will no longer be entitled to exemption under those earlier mechanisms.