_config.yml

GridFieldDetailForm_ItemRequest:
  extensions:
    - GridFieldDetailFormExtension

GridFieldDetailFormExtension.php

<?php

class GridFieldDetailFormExtension extends Extension {

	/**
	 * @var array
	 */
	private static $allowed_actions = array(
		'doLock'
	);

	public function updateItemEditForm(&$form) {
		if ($this->owner->getGridField()->getModelClass() == "Something") {
			$record = $form->getRecord();

			if ($record->status == 'AVAILABLE') {
				$action = new FormAction('doLock', 'Lock vehicle');
				$action->setUseButtonTag(true)->setAttribute('data-icon', 'chain--pencil');
			}
			
			$form->Actions()->push($action);
		}
	}

	/**
	 * Mark a used car as 'AVAILABLE_NON_UPDATABLE'
	 * @see UsedCar->lockVehicle()
	 * @param Array $data
	 * @param Form $form
	 * @return mixed
	 */
	public function doLock($data, $form) {
		$this->owner->record = $this->owner->record->lockVehicle();
		$form->sessionMessage('Vehicle locked successfully', 'good');
		
		return $this->owner->edit(Controller::curr()->getRequest());
	}

}