The Others were originally intended by the producers to be an uncivilized tribe living as simply as their appearance suggested but changed in concept during filming. Introducing the fake beard was a convenient way to cover the retroactive change to The Others.
Very unlikely, because the producers say that the mythology of the show (which would include who the Others were) has been planned out from the beginning.
Very unlikely even if we don't take the producers at their words, because (1) merely having or not having a beard isn't indicative of technology, as the other Others (Ethan, the twins, Ben, etc.) didn't tend to wear beards, and the other islanders seemed perfectly capable of shaving; (2) there were countless indications of technology long before the fake beard was found in "Maternity Leave", beginning with Ethan's use of needles in "Raised by Another", and continuing with their use of boats and guns in "Exodus, Part 2". Perhaps the true identity of the Others wasn't fully conceived of in season 1, but there is no reason at all to believe that the producers ever intended for the Others to really be "hillbillies", as Michael called them. If nothing else, J.J. Abrams, having worked on a series like Alias, would probably find a straightforward, technology-lacking nemesis quite dull.
Recall that there was a strong indication of technology even earlier than there was an indication that there were other people living on the island. Sayid intercepted the Distress signal in Pilot, Part 2, and then found the cable in Solitary, even before Ethan was first shown onscreen. These facts lend more credibility to the belief that the original intention of The Others was at least close to their ultimate realization and not just that of "hillbillies" easily explained away by a single fake beard.
The fake beards are used as an intimidation tactic to get the plane survivors to do what they (the Others) want.
In "Through the Looking Glass", Jack is seen wearing a scraggly beard. This is a subtle means of suggesting that Jack is "pretending" in the real world to be something he is not, just as the Others tried to hide their true nature from the Losties, or perhaps even suggesting that future Jack is not the same "Jack" from the Island. Also note the dialogue in certain scenes from "Through the Looking Glass": when Sarah confronts Jack in the hospital she asks "Are you, Jack?" in regards to his drinking but she places emphasis on YOU...as if to say Are YOU Jack?" And his reply is, "No."
This was directly related to his drinking. She emphasized YOU as in "Are you drinking again, Jack? Are YOU, Jack?"
The others are aware that some people have the ability to move up and down their timeline (e.g. Desmond). Some of the others may also have this ability. They initially wear disguises when interacting with the Losties in case they have to go back in time and interact with them in the past, and don't want to be recognized.
Alternately, the use of disguises prevents a person from being another person's constant.