Modification of key concepts 8 Key concepts may be modified by regulations 20 (1) The Scottish Ministers may by regulations make other provision concerning— (a) who is a chargeable passenger, (b) who is a non-chargeable passenger, (c) which aircraft are chargeable aircraft, (d) which aircraft are non-chargeable aircraft. 25 (2) Regulations under this section— (a) may add, change or remove— (i) any exemption from being a chargeable passenger or chargeable aircraft, and (ii) any provision that defines or otherwise explains a term or expression, and 30 (b) may modify this Act.