MTW v1.1
The castle tactic works with rebels also. If there is a group in the castle bribe them the year after the other province army.
An army in a province takes 2 years to come over but an army in a castle takes only one, so bribe the province army, make sure they accept then bribe the castle garrison and you get a province with army and buildings intact.

The only other time I have ever gotten provinces completely intact is when there is no castle at all, or the enemy abandons the province. Bribing a rebel army in a province will still see them loot it when they take control of the province.