DonovanSorenson:Perhaps there is water all over the place, you might want to change to one of your cheaper balls while playing that hole.
All nitpicking between PGA and USGA aside, the Rules of Golf allow to change the ball on the tee.
But, it must be available there! WGT bags hold only one type of ball, while the others are in the inventory (AKA garage). To go there would certainly be a blatant breach of the Pace of Play Rule! Thus, you don't have any different type available.
As a courtesy, WGT provides ball selling points for your current balls anywhere on the course, as well as free Starter balls as a replacement, but that's it! Inventory is locked to prevent any illegal club changes!
And, from a psychological POV, it's bad to change to a cheap ball in front of water. This means that you accept to fail which, IMHO, means that you will fail. It's better to stay with your best ball and do anything to keep it dry!
In WGTland the difficulty will be obvious: Cheaper balls have different (and weaker) characteristics. Are you sure to pass the hazard with these balls?