In Xcode 3, we worked out (by trial and error) that we could COPY the system templates to a new location (three possible locations, because Apple kept changing it), and customiz
This is only a partial answer to the question, but for anyone else struggling (like me) to work out the "correct" way, here's a workaround that partially works.
Today, with Xcode 4.5.0, the following works:
Customize file/project templates:
~/Library/Developer/Xcode/Templates
(the parent folder should already exist - Xcode4 auto-creates it)[Xcode4.app]/Contents/Developer/Library/Xcode/Templates
[Xcode4.app]/Contents/Developer/Platforms/iPhoneOS.Platform/Developer/Library/Xcode/Templates
NB: in step 2 above, you can also ALLEGEDLY create that folder at:
~/Library/Application Support/Shared/Xcode/Templates
...but that never works for me, and the parent folder doesn't exist with new installs of Xcode 4.5, so I suspect Apple is phasing this out? (since they refuse to document it, I'm just guessing)