!rant
What I tell every Admin Padawan and I hope it will help you, too...

---
Whatever you do on any system, always make sure you know and are able to revert your changes so you can return to the last working system state.
---

It is basically somewhat similar to "always have a backup". But it goes much further in my opinion because it also implies that you know for certain that a recovery works as well since:

"Nobody wants backup, everybody wants recovery"