I like to replace the standard script templates with my own and also add a few custom ones. The script templates I'm talking about are those used when selecting e.g. Create -> C# Script from the context menu in the project window, or form the Assets menu. They are located inside the Unity install folder at Unity.app/Contents/Resources/ScriptTemplates on OS X and at Editor\Data\Resources\ScriptTemplates on Windows. Therein also lies the problem of modifying them… every time you install a new version of Unity, those are not present any more and have to be copied over to the new install folder, or are lost, if you install over the same folder. I wrote a script to place them where they belong for new installs, but through the Unity Hub would be a convenient way to manage these templates and make them available on all Unity versions installed.