I think the question about composing traditional music of the future is not really about whether you can compose something now and pass it off as part of the current tradition. (As "pass it off" is a loaded term, perhaps I should say "insert it invisibly into" or something like that) An easy job to do with a fiddle tune, harder(but possible) with a song.
   I think the question is more about creating the tradition of the future, which is a similar and overlapping topic, but doesnt necessarily imply that you have to include any kind of fake antiquity into the situation.