All optical signal level swapping and multilevel amplitude noise mitigation are experimentally demonstrated using the three gain regions of optical parametric amplification, i.e., linear, saturation, and inversion. The two-amplitude-shift-keying and eight-quadrature-amplitude-modulation optical communication systems with baud rates of both 10 and 20 Gbaud have been employed to demonstrate the proposed approaches. Less than 1% error-vector-magnitude degradation is observed after signal level swapping. For amplitude noise mitigation, a more than 20% decrease in amplitude error is confirmed.