I have an existing app that needs to be compiled for different clients

Each client requires their own icon and splash screen.
I would also like to be able to conditionally include various features depending whether the particular client requires them or not.

I have tried setting up different targets for each client, but not having much luck so far.
The different resources with the same name, but a different path keep getting mixed up.

Ideally I would like to be able to build an app by duplicating another client that is similar and then just make the minimum number of changes to create the app for the new client.

What is the best way to set this app up?