Stretching can acutely reduce hypertonicity, sure. But stretching as corrective exercise is generally not going to have a global effect. For example: stretching your pec minor in the "anatomically optimal" 90 degree pec stretch position is not going to correct the anterior tilt of the scapula. Why not? Because it's anteriorly tilted from using the pectoralis minor as an accessory muscle of respiration, and a stretch is unlikely to correct the breathing pattern.