SO now your argument is that handwaving is the same as creating a PrC and creating requirements no one can attain at the moment... now who's jumping through hoops?
Unless of course their PC dies and they create one born and raised on the Iron Coast. Really we can do this all day, but it seems like this is just you avoiding the fact that there is a difference between creating an actual PrC and handwaving an effect.
This.
Yes, you can certainly do that. But if you do go down the road of making it a PrC-based ability (rather than just assigning a number because you're the DM) and make it just slightly less exclusive, then you can have adventures where the swashbuckler PC is trying to bribe/cajole/trick his way into the pirate community to learn these awesome skills... in some games, that would be a derailment of the plot, in others it could become the plot.
As opposed to flat bonuses per se, the things that explain bonuses -- PrCs, feats, weapon mastery (BECMI), items, etc. -- all offer potential for roleplaying, not just mechanical advantage (which unfortunately is how they are most often used/viewed IME).
And this.
Well, it's a matter of perspective. For some DMs (and some moods for some DMs that do it different ways at other times), "playing by the same rules the players do" is something to be aspired to and enjoyed.
As well as this.
I see nothing wrong with adding such a prestige class/feat/template. Doing so might just offer more to the adventure, or future adventures.