Peter K has an excellent answer on migrating Performance Warehouses here.
So, if the disconnect is planned to take longer than 20 minutes, we recommend to
- install the new performance warehouse
- copy the schema and content of all tables _except_ for the measurement_*, percentiles_* and blmeasurements tables
- disconnect the dt server from the old pwh, connect it to the new one, it'll start writing immediately with the correct metadata
- copy over the contents of the tables you left out before (mentioned above)