Section 12(4) of the Pension Funds Act creates a mandatory obligation on the Registrar to register a rule amendment if (a) the Registrar finds it is not inconsistent with the Act, and (b) the Registrar is satisfied it is financially sound. The section does not confer a broad equitable discretion to refuse registration on other grounds. Section 37A's prohibition on reduction of benefits is qualified by "save to the extent permitted by this Act", and section 12(1) permits rule amendments, including amendments that reduce benefits. The context and associated wording of section 37A indicate it is concerned with reductions from external factors (such as attachment, pledge, hypothecation), not rule amendments. A rule amendment that reduces guaranteed retirement benefits and makes them conditional on employer funding does not conflict with section 37A. Section 14A, which provides for minimum benefits on early withdrawal calculated by reference to guaranteed benefits, does not prohibit reduction of the guaranteed pension itself, only sets the minimum calculation method. Where administrative action (the Board of Appeal's decision) is materially influenced by errors of law under section 6(2)(d) of PAJA, a court may in exceptional circumstances substitute the administrative action under section 8(1)(c)(ii) of PAJA rather than remitting the matter.