No, the upgrade to StratIS is meant to be as painless as possible.
All existing keys will continue working on doors they have access to until the key is replaced.
Each key is replaced individually. For example, if an apartment has 3 residents, you can replace the grey key for just one of them without affecting the others.
In the StratIS App under Places ... the unit you should see each resident listed, and you select which resident you want to replace the key for.
This means residents can continue using their grey key and you can replace a with blue key at turnover or if a key is lost, or whenever you prefer to upgrade them to the blue key.