What's the best way to swap Xcode contents for projects intended for many clients?

I've got a relatively large Xcode project that produces a single app. However, I have many clients/customers who require deep customization and branding of said app. These configurations include different graphics, a few different interfaces and implementations, and, perhaps most importantly, .xcconfig files.

My Xcode project has a dedicated group that points to a particular client's customization folder on disk, so by opening the Xcode project and building, you get a build of the single app with the current client's customizations. To switch to another client, I change where that group points to on disk. (I also change and switch-back the xcconfig "Based On" settings in the project's Info pane to reload the full xcconfig inheritance; Simply changing the group containing one or more xcconfig files doesn't reload this!) This has worked great for 100+ clients. It's a little tedious to switch this folder every time you need to build the app for a different client and ensure the xcconfig is correct, but it works.

Now I'm in the process of automating builds via the command line, and running into troubles. The quick and dirty solution to pointing the aforementioned Xcode group at a different customization folder was to copy the ProjectName.xcodeproj/project.pbxproj file to ProjectName.xcodeproj/project-template.pbxproj and put placeholders inside this file that can be grepped and replaced with the name and path of the desired customization folder. Then, temporarily overwrite project.pbxproj with the modified project-template.pbxproj, and build to get the correct app.

As you've probably observed, the project.pbxproj was duplicated and modified, and will therefore get out of sync as developers modify the original and forget to also update the template. And besides, I shouldn't really be messing with pbxproj files in this fashion anyway -- that's Xcode's private stuff.

So, is there a better way to tell Xcode about a folder full of resources, code, and config files perhaps during the Build Phase with a script or environment variable, rather than at the project group level? The most complicated bit seems to be the xcconfig chain, since each client has their own xcconfig file that inherits from the single app's Debug, Development, and Distribution xcconfig files.

Sorry for the long-windedness of this question, but it's a little complicated! Any suggestions would be greatly appreciated!

I think you would way better off using the targets feature in Xcode. Have one project and the resources of every clients in that project.

You can then duplicate the target you already have (right-click on your target, by selecting the project file in Xcode's Project Navigator).

All your targets will be compiled with the same code. You just need to change the resources in Build Phases > Copy Bundle Resources to have different app created for each target. No need to look at Xcode's internal files.

You can even change the code in your source files by adding a preprocessor macro in your build options (something like FIRST_CLIENT=1) and then look for these definition in your file with #if FIRST_CLIENT.

I have a project set-up like this and it works pretty well :