I've thought a lot about your posts and your situation. My reply is based on my culture (US), and I might respond very differently if I were in HK or elsewhere. I am clueless when it comes to the cultural differences between the two places, which is an important deficiency of mine!
So with that being said, let's pretend that I am the manager of your Lange boutique (or I am the Lange regional manager in that part of the world). And let's pretend that I just learned about your situation by reading this PuristsPro forum thread. So now I know what your expectations were, and how you handled the situation when your expectations were not met. If I have the facts correct, then here is how I would respond as the boutique or regional manager:
(1) I would apologize to you profusely, politely, and personally.
(2) I would immediately order a replacement strap, short length with contrasting stitching, at no additional cost to you. I would have it sent to you or offer to put on at the boutique at no charge -- your choice. I would include a small Lange gift -- a Lange baseball cap or something -- with the strap.
(3) I would insist that you keep the old black strap, as a courtesy -- no need to return it to us.
(4) I would insist that if you ever need to purchase any other Lange timepieces or accessories, then you should contact me directly, so that I can personally provide you with the attention and service that you expect and deserve.
(5) I would do all of the above -- (1)-(4) -- to ensure that you were 100% satisfied with the final resolution of this strap matter.
(6) I would quietly instruct the employees at the boutique that if you ever try to order anything directly from them again, then they should either (1) politely refer you to me, or (2) politely but firmly and clearly explain to you BEFORE making the sale that NOTHING you purchase can be returned or exchanged under ANY circumstances (and we would always write that language on your receipts in the future, no matter how small the item).
(7) I would quietly ensure that we not invite you to any more Lange events (dinners, etc.) -- at least not in the near future.
I would take steps (6)-(7) because I would want to try to put a significant amount of "polite distance" between you and my brand, with the hopes that you would turn your purchasing power away from us and towards some other manufacturer while still feeling generally good about us (because we resolved the strap matter to your satisfaction, and that matter was your last transaction/encounter with us). I would feel this way because almost all customers who were truly upset about a store issue AND who appreciate the value of a long-term, mutually satisfying business relationship would ask to first speak with the manager before taking the extraordinary step of publicly airing their complaints (which takes MUCH more time than a quick conversation with the manager). The rare customer who chooses to publicly air his dissatisfaction on the Internet BEFORE AND INSTEAD OF taking the simple, customary step of first speaking with the boutique manager is one of those rare customers who are not worth keeping. Why? Because from a sensible, practical business perspective, this small class of customers is too risky. They often cost us more business than we get from them. Only a very desperate business would want or need to incur the risk of carrying a customer who posts his dissatisfaction on the Internet before giving the business a reasonable chance to fix the situation, and we're not that desperate.
Would that be an understandable resolution based upon the circumstances? And would you find it fair, though perhaps not ideal?
[Note that I made no mention of Lange's inviting you to "extravagant dinners in
various cities," that "in HK, most places don't accept exchanges," and
that you never
purchased anything from this boutique other than this one strap that you want to return after using it. I'm deliberately avoiding those additional facts because I'm trying to see this through a purely dispassionate economic perspective. I'm not considering factors as goodwill and gratitude that also play a significant role in business relationships.]
Again, I'm viewing all of this from my US-based lens. Cultural differences may play a HUGE role in my current reaction vs. how I might react if we were from the same culture. Also, I mean no offense to you, and I am not judging you in any personal way (I'd bet you're a really nice, interesting guy!). I'm just giving you my honest reaction/response to the facts that you presented as viewed through my lens. And lastly, thanks again for posting this and for starting this conversation -- I think it's really interesting! -- and I wish you the best of luck however it turns out.
PS -- If you want a custom-made strap for MUCH less money than a genuine Lange strap costs, PM me and I can give you a brand recommendation. I have a small wrist too, and Lange "standard short" straps are far too big. You may be better off with a different strap maker. And hey, if you ever visit Boston, I'd be happy to show you some non-Lange short straps on Lange watches.