It's a real pity that no spillover occurs during preset change, if this feature will be implemented it would be a great achievement.
It would indeed be a great achievement, as it would mean that the box had magically doubled its power.
how long is this “brief period” ?
It depends on the algorithm – usually around half a second. The latest software loads faster than the old stuff.
when you say “bypass” do I have to understand that the dry signal only can be heard through the stompbox?
Your understanding is correct.