Switching playing hands in-game?

To be fair, if I were the umpire, I wouldn't know what to do in that situation. I don't suppose that's something they generally cover.

 

I can only concur to the posts here; I have been to a triple-digit number of tournaments as a player, organizer, umpire, technical assistant, and spectator, and have never once encountered such a rule. There is certainly no registration of handedness in any official BWF (or German) tournament.

So the interesting question is: How can such a rule exist, and can it be enforced in any way?

The tournament organizers or accredited press can ask you to fill out a questionnaire for **promotional** purposes. For instance, BWF mandates players to be available for interviews in §4.3 of the Player's Code of Conduct and §1.4 of the Player Commitment Regulations.
These promotional materials do not have any bearing on the game; if you say *weakness: serve* and win the match with 42 immaculate serves right on the line, you're of course not being punished. You can decline to answer or answer "I do not want to give out that information lest it advantages my opponents".
However, §4.2 and §4.3.3 of the BWF code of Ethics could be interpreted as requiring players to be somewhat serious in media communication.

But how about having an actual rule requiring to play with a preregistered hand?

Any official tournament where top-level players can participate must be sanctioned by BWF, who will require the use of official laws. Similarily, official tournaments of the federation (say, regional or district-level championships) have to be sanctioned by the national federation, which will require their translation of the BWF laws as well. For more information on sanctioning, refer to §§3-4 of the General Competition Regulations.

However, anyone can of course organize a private tournament without any affiliation to any official badminton organization. There, the organizers can make up their own laws - if someone wants to play under blacklight, with heavy training rackets only, or play a round of chess after every game, nobody can hinder them to do so. However, international-level players are generally forbidden from participating in these tournaments. This must be the kind of tournament you were playing in.

 

This may seem difficult to believe, but it is not any particular advantage.

If anything, the 2nd racket gets in the way.

 

There is no explicit rule against holding two rackets at the same time. Therefore, when it actually happens in game, umpires don't call fault.

However, the laws make it clear that one racket is expected, at multiple times they talk about the racket of the player.

The rules just forbid behavior that was seen as detrimental to the game. Situations that never came up are not covered. Just like there is no explicit rule against bringing a fan to blow all the shuttles back over the net, or playing with spring-powered shoes, there is no rule against coming on court with a racket in every hand.

In any case, as @Charlie-SWUK said, having two rackets is probably more of a disadvantage than an advantage:

• Valid serves are close to impossible - one of the rackets will initiate the serve way too soon. You'd basically have to grip both rackets together in one hand.
  
• Shot quality will be diminished since it is harder to balance.
• Movement on court will also be harder with a second racket to worry about.
• The second racket will get in the way, and will be hard to coordinate.
• Playing backhand (for instance on defensive shots) will be really hard.

So the players who try this will lose against even opponents.

If a player tried this in the tournament, the referee would likely cite some generic spirit of the game law like §4.2.2 and §4.2.6 of the Player's Code of Conduct.

Since nobody (as far as I'm aware) has done this, probably due to the disadvantages listed above, there is no need for regulation forbidding it.

 

The trick shots generated would be great though with two rackets!