You can define indentical UDEs on multiple operations by selecting them in the Operation Navigator, MB3, Object, Start Events. There is no OOTB way to mass edit existing UDEs. From inside each operation dialog, you can also copy UDEs from another operation. What exactly are you changing? There may be a way to inherit the parameters instead of using UDEs.
You can mass edit feeds from the Operation Navigator. You can also inherit them from a method. We tend to focus on using machining data libraries for feeds, speeds, depth per cut, stepover; rather than mass editing.
If you are doing this a lot, there is an API for UDEs, so it might be worth the effort to write a journal.