Magento: Override the core files of Magento

We have a very simple way to override any core file from the Magento without any affect on core file.
Just copy the file and paste in to local folder of path  app/code/local/ with the same file structure(same mimmic of core file structure).

For example:
Suppose we want to edit the Grid.php file of path: \app\code\core\Mage\Adminhtml\Block\Sales\Order\Grid.php
Now just edit Grid.php and paste it into the local folder of  path: \app\code\local\Mage\Adminhtml\Block\Sales\Order\Grid.php

That's IT..