The intention is that letting the knife-edges make their own trench in the seal material gives you the closest possible fit. Eventually seals and other things start to wear and more air will leak forward through the engine, reducing efficiency.
Making a larger trench theoretically means lower efficiency, but that's only in one stage. The overall effect might be very small. It might be zero insofar as the performance after x hours or cycles is the same as it would have been without the mod.
The longer-term concern is whether the root cause (the fact that flexing of the engine wasn't accurately modeled or found in flight-sciences testing) will bite us later.