The idea to humidify old, dry, or brittle shuttles is nothing new. So many people steam the shuttles before play. The way many go wrong is that they steam the shuttles too close to playing day, or steam them too intensely. You don’t want the shuttles to be wet or moist when you play with them, or they will turn floofy and slow in a few rallies. So it’s best to do it a few days in advance. First, the feathers will take in the moisture, but then they should also be allowed to dry. Many people let the steam run through the tube and then close it, this could keep the shuttles wet for too long.
I advise to take all the shuttles out of the tube, individually hold them in the steam (of a water kettle for example) for a few seconds, rotating the shuttles so all sides catch some steam, and then briefly let the steam go on the ‘inside’ of the shuttle. Stand the shuttles somewhere out of the tube to dry properly before putting them all back.