Rest_command formatting

I need to use REST commands for a PC windows server. I’m using the following:

  rest_command:
    arcade_volume:
      url: 'http://192.168.0.89:7900/preDefined?operationName=System.Volume.Change&value=20'

Two questions:

  1. Is it possible to change the “20” value using automation? For example - I want to input_number slider to send this command with the value as parameter

  2. Is it possible to use something like a global variable instead of using the server address directly (“192.168.0.89:7900”)? Since I will have several commands using the same address I want it to be set from just one place.

just a remidner…