Nothing contained in the regulations in this part shall be deemed to affect or limit the right of a customhouse broker, licensed as such by the Commissioner of Customs in accordance with the regulations prescribed therefor, in any customs district in which he is so licensed, at the office of the District Director of Internal Revenue or before the National Office of the Internal Revenue Service, to act as a representative in respect to any matters relating specifically to the importation or exportation of merchandise under the customs or internal revenue laws, for any person for whom he has acted as a customhouse broker.