Duplicate a Material? (Project Window)

I want to duplicate a Material in Unity to make some changes, how can I do this?

When right clicking on most stuff in the Project Window I can select a copy option, but not when performing a right click on a Material also copying via keyboard shortcuts is not working. How can I avoid restarting from scratch every time?

I think you are confusing some things here. There is no “copy” option in the right-click menus of the Project window. The copy&paste options are available in the Hierarchy window, though.

Using the Ctrl+d shortcut will duplicate any object, though, both for assets in the Project window, and scene objects in the Hierarchy window.