Just to clarify a bit. When you buy a license, you use it to activate, or unlock VC. You don't need to reinstall, and everything should remain the same, including your custom commands. The only differences are, no limit to the number of commands, and removal of the demo text at the top right.
In fact, you are really unlocking your entire PC when you activate, so if you have multiple installations of VC they will all be unlocked.
As Kalle says, you can backup you custom commands a number of ways, and it is always a good idea to back them up from time to time, or when you are about to make a change, like upgrading to a new version. Because the entire installation folder of VC is so small, my preferred method is to copy or zip up the entire folder as a backup. If I want to try something new, or create. A special customization just playing a video game for example, I will usually create a new folder to experiment with. This is part of the beauty of the portable installation approach and the reason VC does not use a standard installer which creates a folder in program files, and then stores data elsewhere. Everything is "under one roof" , although technically this is only true if all your references to external files use relative paths.
