There is no special provision update mode in the framework. If you call the provision method on a field for example, then the field will be provisioned with the current definition attributes and properties that are set in code on that specific field declaration.
The same applies for content types and list instances.
I know feature supports upgrade but i think that is simply another event method in the feature reciever that will be called. You can call the provision method from that reciever if you want to perform upgrade from there. However, i need to
do some further investigation on the last one.
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