Different regulations may be made under paragraph 3 above in relation to different classes of persons, and any such regulations may be so framed as to have effect as from a date prior to the making thereof, so, however, that so much of any regulations as provides that any provision therein is to have effect as from a date earlier than the making thereof shall not place any person other than the Agency in a worse position that he would have been in if the regulations had been made to have effect only as from the date of the making thereof.