Change templates in Xcode

You wouldn't change the existing templates. In other words, don't modify anything under the /Developer hierarchy (or wherever you installed your developer tools).

Instead, clone the templates you want to have customized variants of. Then change their names and the information in them. Finally, put them in the appropriate location in your account's Library/Application Support folder, specifically:

• File templates: ~/Library/Application Support/Developer/Shared/Xcode/File Templates/
• Target templates: ~/Library/Application Support/Developer/Shared/Xcode/Target Templates/
• Project templates: ~/Library/Application Support/Developer/Shared/Xcode/Project Templates/

That way they won't be overwritten when you install new developer tools, and you can tweak them to your heart's content.

UpdateFor newer versions of Xcode the updated path will be:~/Library/Developer/Xcode/Templates/File Templates/Source

This may be useful for somebody:

As for XCode 6 to XCode 9 the file templates are in:

/Applications/Xcode.app/Contents/Developer/Library/Xcode/Templates/File Templates/Source

Update:As @carbo18 noted, it's proably better to create the directory ~/Library/Developer/Xcode/Templates/File Templates/Source and put your custom templates there. The best way may be to use as base one of the ones in /Applications/Xcode.app/Contents/Developer/Library/Xcode/Templates/File Templates/Source

Xcode uses template files for file and project templates and does variable expansion in both at creation time.

Xcode 3.0 templates can be found in [Dev Installation]/Library/Xcode/, likely /Developer/Library/Xcode. If you want to modify these templates or add your own, use the following directories to save your new/modified templates so that they are not wiped out by future Developer Tool upgrades:

• File templates:~/Library/Developer/Shared/Xcode/FileTemplates/
• Target templates:~/Library/Developer/Shared/Xcode/TargetTemplates/
• Project templates:~/Library/Developer/Shared/Xcode/ProjectTemplates/

I think that you can also use the /Library/Developer/Shared/Xcode/[File|Target|Project] Templates/ directory for templates shared by all users.

If you just want to change the MyCompanyName in the templates, the following command line will do the trick:

defaults write com.apple.Xcode PBXCustomTemplateMacroDefinitions '{ "ORGANIZATIONNAME" = "NewCompanyName";}'

A good tutorial on writing file templates is here [MacResearch.org].