Hi,
To the best of my understanding "Org By Period" is usually approached in a couple of ways.
1. The neccessary parent/child relationships can be represented within the current Entity reporting structure. So, if any entity is moving division in Period 3, you can set to 0% consolidation and add a relationship for the entity under it's new parent at 100% consolidation. This results in a single entity hiearchy, which is quite efficient but it may confuse users since the base entities will appear until multiple parents. I don't believe there is a way to hide the inactive relationships.
Reporting is also impacted since there is no standard way of recording that a relationship between a parent and a child entity is inactive. This means a member filter such as E#Division.Base would return all active and inactive entities. As a result, custom member lists are deployed but these don't typically work on all filter expansions and as such your reporting options become limited. It also means the standard Drill-down functionality in the system doesn't quite work as expected to the extent where if an entity in no longer consolidating into it's parent because it has moved it will still display in the Drill down results.
Other considerations with this approach are the fact that custom consolidation and eliminations rules are often needed.
2. The second approach, which I'm sure you are familiar with, is to create an alternate hiearchy outside the current entity reporting structure.
Lee