Basically if you use cocoapods (like everyone else these days..), all used Pods get built into a static library. The actual project just references this library. So you cannot overwrite any defines within the pods, because they get compiled separately.
It would be nice to set custom loca keys via an API (like [Appirater setLocalizationKeys:@{AppiratorTitleKey:@"my_custom_title_key", ...}]). Or at least a custom loca table (so smth. else is used than AppiraterLocalizable.strings). The Idea is just that you do not need to touch your code at all.
The simplest solution for now is to build a custom podspec (eg. as a gist) without your loca ressources and then reference it in the Podfile via :podspec => 'www.foo.bar/customspec.podspec'.
When you do it that way, you can use your own AppiraterLocalizable.strings files, while still using Appirator as a pod.