How can I hide the cautionary key signatures after an instrument change. At my example: a Clarinet in A changes to clarinet in B. But the first entry of the “new” clarinet is about two flows later, so there is no need to show this change in the score. Especially when the main key is A major, so after the change to the clarinet in B there are five crosses given 
AFAIK this is not possible now. I always prefer to have the key signature change right at the next entry as an additional reminder to the performer that they are on a different instrument. Daniel has said they plan on “early” or “late” options for this in the future. Here’s the thread where he commented on this:
Oh, ok, thanks a lot for the quick respond. Too bad that this is not implemented right now, just the next thing, why Dorico is not ready for professional use, for example with music publishers… Let’s wait what will come in the future…
Dorico may not be ready for YOU to use in your professional work. Plenty of professionals have had excellent success with it for some time now, myself included.
I don’t disagree that there are features that need to be added. No one does. But I disagree with your blanket evaluation. Every program has its quirks and workarounds.