JD......If someone appeared at a re-enactment with this garb, would you tell him it is "improper", you cannot participate?
Don
Nope, not unless he asked for a critique.
Then it would be up to him to decide if he participates.
One might be refused admission to a juried event, If he were to attempt to register using spurious documentation for one's uniform, or any clothing and equipment, for that matter. The authenticity committee would make the determination of what is correct for that particular event. Otherwise, it's up to ones commanding officer, or the units authenticy committee to decide what standards they want to implement for participation in their unit.
If someone wants to look Rangery, on his own, but does not claim to be something ridiculous, that's ok too. IMHO it all depends on the event. A character dressed up like Teddy Roosevelt was once asked to leave a pre-1820 rendezvous, for example. Who or what participates in a particular event is up to the organizers.
On a personal note, I once read an article by Allan Gutches, I think, that presented the idea that reenactors who do not accurately portray their chosen persona are, in effect, lying, visually, and often verbally to the public who depend on said reenactors to present a realistic impression of their chosen persona. IMHO, a Rogers ranger reenactor who portrays a member of one of the compnies raised after the issue, for example, while wearing a green Ranger uniform is, in effect lying about who and what he is supposed to be.
That same reenactor portraying a member of a company raised after the uniform issue while wearing civilian clothing, who can explain why A Rogers' Ranger is wearing civilian clothing and carrying a civilian firelock, hunting pouch, and horn would, IMHO, be as correct as a modern day historian/reenctor can be. Moreover, he would present an honest portrayal to the public, as well as setting the bar a little higher for other "reenactors".
Unfortunately, most folks would only refer to such a dedicated researcher/reenactor as an "authentinazi" or "thread counter", rather than recognize his dedication to the sport.
God bless