Reducing excessive launch switching activity (LSA) is now mandatory in at-Speed scan testing for avoiding test-Induced yield loss, and test set modification is preferable for this purpose. However, previous low-LSA test set modification methods may be ineffective since they are not targeted at reducing launch switching activity in the areas around long sensitized paths, which are spatially and temporally critical for test-Induced yield loss. This paper proposes a novel CAT (Critical-Area-Targeted) low-LSA test modification scheme, which uses long sensitized paths to guide launch-Safety checking, test relaxation, and X-Filling. As a result, launch switching activity is reduced in a pinpoint manner, which is more effective for avoiding test-Induced yield loss. Experimental results on industrial circuits demonstrate the advantage of the CAT scheme for reducing launch switching activity in at-Speed scan testing.