Use pre-set callback to modify mapped parameters

[tylerjw]

When the key field changes, the pre-set callback could be used to declare/un-declare mapped parameters. This assumes that you can declare in the callback and that won't cause a deadlock; this requires testing to verify. Reference to the docs on pre-set callback:

https://docs.ros.org/en/rolling/Concepts/Basic/About-Parameters.html#parameter-callbacks