How to override default URL on Edge Micro Gateway?

[#1]

I have one MicroGateway aware proxy defined and downloaded in to Edge MicroGateway with these defaults:

proxies:
  - max_connections: -1
    name: edgemicro_weather
    revision: '1'
    proxy_name: default
    base_path: /weather
    target_name: default
    url: 'https://weather.yahooapis.com'

Let's say for some business reason based on payload condition I want to override the target URL from https://weather.yahooapis.com to https://legacy.weather.yahooapis.com.

How do I dynamically create backend URL which overrides the default downloaded one?