This feature in my opinion should be implemented in Xcodeproj directly. If we generate two xcconfigs (one for import and one for building) we could implement:

``ruby
def save_as(pathname, prefix = nil)
  pathname.open('w') { |file| file << to_s(prefix) }
end
```

Then #to_s should forward the optional prefix (a string) to #to_hash which is needed maps the generated hash to a new one where the keys are prefixed.

Related: CocoaPods/Xcodeproj#68