In such scenarios, the best practice is to create a Custom Command with all the necessary actions and conditions, and then execute it by both the Business Rules. In this case, you will need to maintain only the Custom Command.
For information on how to create a Custom Command, see Create a Custom Command. To execute it in your Business Rules, use the Execute a Custom Command action.
In order to avoid running the command manually from the UI, you can disable it. Disabled Custom Commands do not appear anywhere in the UI and can be executed only by Business Rules, Scheduled Tasks and other Custom Commands.