How do you flavour you weapons?

[Psyren]

That's not flavoring, though. You're adding mechanical benefits to the weapon.

The thing that is a mechanical benefit is making your hands free to do other things. That part does go beyond flavoring.

+1
If you wanted to make a pair of custom hand crossbows that left your hands free I would probably let you do that, but it would most likely require a quest of some kind.

OT: My go-to weapon flavors are things like eastern weapons, like turning a halberd into a naginata or a greatsword into a nodachi or a whip into an urumi. I never liked the idea in previous editions of eastern weapons being "exotic" and needing a bunch of extra bandwidth to remember how they're different when a simple reflavor would do.