hook_options_list not getting fired in a custom module
You can use hook_field_info_alter() to attach custom allowed_values_function to your field and implement your own logic there:

function my_module_field_info_alter(&amp;$info) {
  $info['my_field']['settings']['allowed_values_function'] = 'my_module_my_field_allowed_values_callback';
}

function my_module_my_field_allowed_values_callback($field, $instance, $entity_type, $entity) {
  // Custom logic
  return $values;
}