I've never had a Tyros, but from reading posts from Tyros owners in multiple forums, I get the impression that a lot of problems with smoothly changing from one Registration to another tend to be caused by differences in the system effects-- the Reverb Type, Chorus Type, and DSP Type.
As long as you can change Registrations during a few moments of silence-- that is, there are no sustained notes-- the change should occur smoothly, since there are no sounds playing.
But if you need to change Registrations while notes are being sustained, you may have to live with the lack of a smooth transition, although there are some things you could try:
(1) Use the "freeze" feature to freeze any settings that don't need to be changed, so loading the new Registration doesn't try to change any settings it doesn't need to. This might help the Registration load more quickly.
(2) Don't change the system effects types or system effects parameters while sounds are being sustained.
(3) You can change insertion effects on the voices, or the effects send levels on the voices, but try not to change any settings for the voices which are being sustained. For instance, if you're sustaining notes played with the Left voice, but no notes are being sustained with the Right1, Right2, or Right3 voices, then it should be safe to change the Right1, Right2, and Right3 voices, but not the Left voice.
(4) See if you can split up a series of changes across multiple Registrations. For instance, if you need to change the Right1 voice while continuing to play smoothly with the Left voice, set up a Registration that will change the Right1 voice but leave the Left voice untouched. If you then need to change the Left voice while playing smoothly with the Right1 voice, set up another Registration that will change the Left voice but leave the Right1 voice untouched.