The simple answer is, generally, no.
While there is no general offence of impersonating a member of the Armed Forces, and many actors do so in theatre and films. It is similarly not wrong for a civilian to wear uniform or former military clothing for their own preference or entertainment, as long as they are not claiming to be a member of the Armed Forces or hold a rank they are not entitled to.
It is, however, an offence under the Official Secrets Acts to wear Service uniform for the purpose of gaining admission to a prohibited place or for a purpose prejudicial to the safety or interests of the State within the meaning of the Acts.
The unauthorised wearing of Service uniform in this way or the wearing of uniform in a manner that is likely to bring contempt on to it, are criminal offences which may be punished by a fine or imprisonment.
Someone who gains commercial or financial advantage from a misrepresentation of a Service position would almost certainly be committing an offence and may find themselves the subject of court action against a charge of committing fraud.
Even without resorting to the criminal law, most employers would react adversely to someone who gives a false impression, either by statement or dress, of a former Service career they did not have, in order to gain employment or promotion. Any person found out in such deceit could reasonably expect to be dismissed.
FOI 2017/06020 dated 23 June 2017.