Customizing the portal consists of officially supported customizations, and customizations that can be done, but are not officially supported. In this recipe, we will cover both.
The main difference between the officially supported customizations and other types of customizations is that the official ones are guaranteed by Microsoft and will stay intact through updates and upgrades. Any customizations not on the official supported list may not survive an update or upgrade; therefore it is critical to back them up.
Here is a link to Microsoft's blog on the officially supported customizations: