The parameters of a router should be configurable at runtime.
The API is extended with a configureInstance entry point that is called when the parameters of a router are updated. How the changes are applied and when these changes take effect depend on the router and how it implements configuration reloading.
For the most common router modules (readwritesplit, readconnroute), the parameters take effect for new sessions only. This keeps the behavior consistent with server additions and removals.