Hi Henning,
are you having a problem that the tempo is changing when you are changing registrations and you don't want that?
In that case:
Push the "direct access" button and the the "freeze" button
Now check only "Tempo" in the window.
Each time you are changing registrations now, the tempo will remain the same as long as you push the freeze button before you change to a new registration.
Also, as you already said, you must have the "tempo hold" or "tempo lock" in the style options.
If your registrations don't contain styles in theme, for example they have only voices, then resave the registrations one by one and uncheck the tempo.
In that case the tempo of a registration will always be the tempo of the style you choose
If the registrations have a style and you want to choose a different style while playing, the "tempo hold" or "tempo lock" are enough to keep the same tempo until you change to a new registration which has a different tempo.
If you are not having a problem at all,never mind of what I have written
Keep it up Markus!