Regulations may provide that the provisions of this Act and of regulations thereunder shall apply to -
(a) schemes with external members, or
(b) external schemes, or
(c) schemes where the majority of the trustees are not resident within the State,
with and subject to such modifications as may be prescribed and such regulations may require persons other than the trustees of such schemes to carry out in relation to those schemes any of the duties imposed upon trustees by this Act or by regulations thereunder.