Notepad++ to recognize custom file extensions

As many others, I am using Notepad++ as an editor to modify many XML files, which may have different extensions than XML. Such files may be configuration files for ASP.NET or MSBuild files. By default, when I opened them in Notepad++, I saw no syntax highlighting, everything was just black and white. In order to turn the highlighting on, I needed to explicitly select XML as a language each time when I opened such files.

However, using the following link, I just set extensions to what I needed.

http://www.mattblodgett.com/2007/11/notepad-tip-syntax-highlighting-for.html

So I have those files immediately recognize as XMLs when I open them