Regarding URL change in Existing keyword recording

Functions that reside in other scripts, and that are linked with USEUNIT, effectively become part of the current script.

You can call them "dynamically" as in your first example like so:

//USEUNIT My_File
function test(){
  var functions = ["button_one", "button_two", "button_three"]
  for (var i = 0; i < functions.length; i++){
    var button = My_File[functions[i]]();
    button.Click()
  }
}