David Thorpe wrote: “Whilst kilted, I am proud and quite content to wear the retainer's badge of my Chief's arms.”

Well, David, you are fully entitled to do this. But wearing your own crest would not be an expression of disloyalty to your chief. In fact, it would indicate more prestige for him, since he now has another armiger in his following.
(Wearing any other part of the arms is not generally done in THCD, but there is a sporran maker in Britain who will put your shield, engraved in silver, on a specially made sporran.)
When I was in Cape Town in January, the Scottish outfitter there showed me a badge he had had made for a customer who wanted to display his own crest. The crest was a separately cast piece of metal, made to be added to a metal circlet. The interesting thing about this circlet was that it had no wording on it (a motto is usually placed there), but just a decorative pattern.
This means that if I order a similar badge, the silversmith would not need to make a new cast for the circlet, but simply re-use the existing mould. Only making a smaller mould for my crest would be a much less expensive way of producing a unique badge.
Regards,
Mike