Can I change the value of a substitution later in the YAML file?

[aceindy]

Have a a look at select:

@aceindy

# Select.
select:
  - platform: template
    name: "Fan mode"
    id: ${node_id}_select_fan_mode
    icon: mdi:fan
    optimistic: true
    options:
      - Auto
      - Low
      - Medium
      - High
    on_value:
      then:
        - lambda: |-
            auto call = id(${node_id}_my_climate).make_call();
            call.set_fan_mode(x.c_str());
            call.perform();

and then the template it is used in:

@aceindy

  - platform: template
    name: ${friendly_node_name} fan mode
    id: ${node_id}_fan_mode
    internal: true
    update_interval: 10s
    lambda: !lambda |-
      if (id(${node_id}_my_climate).fan_mode == 2)
      {
        if (id(${node_id}_select_fan_mode).state != "Auto")
        {
          auto call = id(${node_id}_select_fan_mode).make_call();
          call.set_option("Auto");
          call.perform();
        }
      }
      else if (id(${node_id}_my_climate).fan_mode == 3)
      {
        if (id(${node_id}_select_fan_mode).state != "Low")
        {
          auto call = id(${node_id}_select_fan_mode).make_call();
          call.set_option("Low");
          call.perform();
        }
      }
      else if (id(${node_id}_my_climate).fan_mode == 4)
      {
        if (id(${node_id}_select_fan_mode).state != "Medium")
        {
          auto call = id(${node_id}_select_fan_mode).make_call();
          call.set_option("Medium");
          call.perform();
        }
      }
      else if (id(${node_id}_my_climate).fan_mode == 5)
      {
        if (id(${node_id}_select_fan_mode).state != "High")
        {
          auto call = id(${node_id}_select_fan_mode).make_call();
          call.set_option("High");
          call.perform();
        }
      }
      return id(${node_id}_my_climate).fan_mode;

(see the whole yaml [here])(Midea branded AC’s with ESPhome (no cloud))

You can also change this in the web interface