How do I make my phone fully customizable?
The Hodor trick is done using this Hodor Xposed module, which requires Xposed framework.

For a rooted device, installing Xposed is indeed a good way to customize without stepping into the realm of custom ROMs, but it comes at the usual risk of bootlooping and other problems. If you're only looking to do it for fun, and have no idea of how to recover from such failures, I advise you against it.