Whenever I create a new .cpp/.h file in Xcode a comment is added to the top of the file. For example:
/*
* .cpp
*
*
Don't edit anything in /Developer as Apple can overwrite this at any time.
The following works for Xcode 4, 5 and 6 except later source differs and is under /Applications
Instead copy the templates that you want to change from /Applications/Xcode to ~/Library/Developer/Xcode/Templates/File Templates and then edit the files keeping the same directory structure but edit the directory name that is the template to not show up a a duplicate in Xcode.
e.g for a new category of C/C+ files in Xcode 5 copy /Applications/Xcode.app/Contents/Developer/Library/Xcode/Templates/File Templates/C and C++ to ~/Library/Developer/Xcode/Templates/File Templates/GPL C and C++
this process is copied from Red Glasses's blog
For Xcode 4 the source path is or for Xcode 4 /Developer/Library/Xcode/Templates/File Templates