yes aptasia-x will kill them. Also kalk paste, lemon juice and possibly peroxide. Turn off your pumps and then inject them. If you do it when the lights are off and the other corals are closed up it will reduce the chance of harming the other corals.
Sometimes just scrubbing them with an old toothbrush will kill them. But it may also spread them as well, so be careful.
Yellow polyp's (Parazoanthus gracilis) IMO are as bad as Aiptasia . They tend to spread by growing in the rocks rather than over them. I am not sure what other corals you have but a Klein Butterfly will wipe them out or any pest anemone killer should work
If you do that, i would plan ahead and think of corals to place in the holes that you are cutting....you can cut to shape/size when removing yellow polyps.