EventSourcing and evolving behavior

Have anyone dealt with a scenario where the rules and behavior of an entity changes over time and combined
that with eventsourcing?

e.g. before 2010-01-01 there may be one set of rules, and another after that point.

And if you revert state of the entity, you might have to revert the behavior also.

I guess this is simply a case where you can keep old behavior in the entity and apply some "if data > xxx then ..."

Just wanted to hear if anyone have done this and how it turned out.

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