Clipping blade tips is indeed a long-honored practice to fix fatigue vibratory problems. I can't count the number of engines that have had this implemented.
But there is ALWAYS a performance matter to be considered; that's why the blades weren't built that way in the first place.
Clipped blades mean the on-wing life is reduced because the engine will run out of EGT margin sooner.
Trust me, if the F136 is cancelled, Pratt will have no incentive to quickly and properly fix the F135.