Unit test your code! If a superclass changes behavior, it will likely break a unit test, so you know you messed up and you know to correct the offending subclasses.
If it broke functionality in your application, but not one of your unit tests, then your unit test coverage is not good enough, or you've missed some scenarios.
That's the number one thing you should do before any kind of refactoring! Unit test, unit test, and again unit test!
If you're not using a fancy IDE try to find a file manager that offers text search functions.