State of the art agents don't usually need such fixed guidance anymore. I've been using Opus 5.5 with Xcode and simply prompting things like "make sure all of our test Suites use the .dependencies modifier, but only if they use dependencies internally" or "make sure none of our test methods are @MainActor, just access the necessary state using standard concurrency constructs". For larger changes, providing the examples you want is often enough to get it most of the way, or even all the way, there. I've had simples prompts for things like "move all standalone SwiftUI view that seem reusable to our Design framework, and create a list of those which can't be moved without effort, listing by complexity".
Overall, there's much less need for prompt skills anymore. They're still very useful for things like best practices, or things you need to make as reproducible as possible, but big skill and planning sessions aren't nearly as necessary anymore.