For Bohemia, I thought of Poles allying with the Czech rebels instead of Austria in the Battle of the White Mountain in exchange of the Polish inhabited parts of Silesia going back to Poland.
The Huguenots successfully have a king convert and the Winter King of Bohemia does not lose to Austria, expect to see a very interesting thirty years war.
They don't necessarily need a king to convert - they had Henri IV on their side (for awhile, at least). But he needs to somehow capture Paris without needing to convert to Catholicism, which is very difficult.