esphome/devices/dimmer_serial_no.yaml

text_sensor:
  - platform: template
    name: 'Serial No.'
    lambda: |-
      std::string mac = get_mac_address();
      return "dim" + mac.erase(0, mac.length()/2);
    icon: mdi:expansion-card-variant
    entity_category: diagnostic
    update_interval: 10m