There is no one-size-fits-all template without defining several variables which require the same amount of insight that you are looking for.
Companies like TCS have developed their own best practice in this realm, details of which I cannot divulge. Perhaps someone in your company can provide you with a best practice example.
Some tools might be available for purchase to help with impact analysis as well (e.g., Natural Engineer). If you have nothing in-house to use, you might look outside for one of these tools.