How to use a “private” .xcconfig in a “Shared” (gi

Question

Often, I'll use an existing .xcconfig in some submodule, to ease the integration of some git submodule (or one of my own Xcode "sub projects") within an Xcode workspace (or project).

This works great, and reduces the need to make lots of local configuration changes to a project which might exist happily on it's own, or which I want to push contributions, upstream to (changes which are unrelated, and indeed wholly separate to settings introduced from the .xcconfig).

However, even without adding the .xcconfig to the project's folder... entries similar to the following..

+7B3453E018A38FAD00D28DF5 /* Mac-StaticLibrary.xcconfig */ = {
    isa = PBXFileReference; lastKnownFileType = text.xcconfig; 
    name = "Mac-StaticLibrary.xcconfig"; 
    path = "/local/AtoZ.framework/AtoZAutoBox/../../xcconfigs/Mac OS X/Mac-StaticLibrary.xcconfig"; 
    sourceTree = "<absolute>"; 
};

and

+ baseConfigurationReference = 7B3453E018A38FAD00D28DF5 /* Mac-StaticLibrary.xcconfig */;

get added to the tracked changes inside the $(PEOJECT_NAME).xcodeproj/project.pbxproj file, by git.

Is there ANY way to keep these modifications to the .xcodeproj "local"? I hate to sully pull requests and project independence with these obviously inappropriate changes.. but would miss the convenience and functionality that this integration method offers... Any advice..