Setting the "State" field with a URL param, that then generates a random address for that state

It’s definitely possible.

1. Create a schema Mockaroo - Random Data Generator and API Mocking Tool | JSON / CSV / SQL / Excel
2. Then create an API. The Handler Script can be as simple as this:

schema "GET State"
set("state",states:params['states'])
generate 10

3. Call your API
   https://my.api.mockaroo.com/get_state.json?key=xxxxxxx&states=Texas

This should give you an idea of how you can accomplish your request.