I was recently asked: “We are migrating to a new country wide data model. Can we keep our historical data in the same database with the new model”
You can import a new model on top of an existing one, and disable the categories/attributes from your old model that are no longer valid. This works well if the two models are consistent with each other e.g., they shared common elements and most of the differences were due to capturing different types of information or different level of data.
If the old and new model are different ways of understanding your world, you should evaluate creating a new CA. This keeps thing clean and avoids people having to interpret reports by trying to remember where you cut over to a new model. You can always query across the old and the new CAs for metrics that are meaningful, e.g. patrol effort.