I haven't brewed this before, and actually added it to my list of planned brews yesterday. However, since the Centennial is being used here primarily as a bittering hop, I don't see why not. If the Centennial was a late addition, I wouldn't do it, because Magnum doesn't impart any aromas. However, after 60 minutes in the kettle, neither will the Centennial. If you are concerned about the aroma due to this replacement, you could increase the flameout Cascade addition by a half ounce.
Magnum typically has about 25% more alpha acid content than Centennial, so you might want to check the IBUs to make sure it's still in a range you want, or adjust accordingly.