I'm sure one could come up with a situation that would break the refluffing. For example there is a sword lying around and someone uses a mind control spell to attack with it or something. Or there could be some bizarre situation where the fate of thousands of people depended on your character defeating a bad guy alone, the bad guy was immune to normal damage and there was a magic sword that could hurt them, thus it would be pretty jarring if your character didn't break their wow. But of course neither of those are likely to arise unless the GM intentionally tries to cause your refluffing to to become a problem, so in practice non-issues.I agree that it's easier just to handwave the situation I was describing, but I'd actually prefer to adhere strictly to the rules. I might say something like, "I'm worried about a loose stone collapsing on my companions, so I use my bokken as shoring and leave it behind." Or whatever.
And the reason I think it's important is so that there's a clear boundary. In the 5-Int Genius thread, Max kept throwing these scenarios at me, along the lines of "Well what if you're in a Zone of Truth and..." He was trying to find a way in which the alternative interpretation would cause actual rules to get broken, in a way that would give unfair advantage.
Or another example is the proficiency: in my fluff the only reason I'm not using a real longsword is that my sensei hasn't given me permission. If we take that fluff at face value, there's no reason I couldn't defy my sensei and pick up the real thing, even though that would break the metagame rules. But since I have zero intention of trying it, the rule remains inviolate.
I think that if you're going to play around with re-fluffing, it's important to be diligent about adhering to the rules.
But here is how I would approach this differently. If the fiction is that your character knows how to use the sword but just doesn't, and I as a GM approved that, then that's how it is, and if some bizarre situation arose where your character absolutely has to use the sword, then they will have the proficiency. And same with any refluffing. I treat them as houserules. Once the fluff is changed, then that is the fluff that informs the rules from now on, and in some rare situations that may lead to different rule-results than the original fluff would have.
The bokken is a complete non-issue. Whether the wooden stick is four or six feet long doesn't matter for its combat stats because there is no sufficient granularity to differentiate between them in that context. But in fiction the bokken has certain length, and in situation where such matters, that's the length used (like whether it fits somewhere, can be used to reach something etc.)Maybe I'm not understanding what you mean here, but I don't see it as disassociation of the rules and the fiction at all. It's just swapping in a different fiction that is still tightly associated to the rules. E.g. my wooden sword. It still follows all the same rules in the same way, it just has different fluff.
But I want the rules to describe thing in the fiction in (somewhat) consistent manner and in any improvisation situation further ad-hoc rules flow from the fiction.