In this paper a linear model is presented and used to interpret the active applications of an external static or rotating poloidally symmetric perturbation to a reversed field pinch plasma. The plasma response is evaluated considering also the sidebands generated by the current distribution produced by the coils. We evaluate the plasma response, obtaining information about mode coupling. In 'quasi-single helicity' states—in contrast to 'multiple helicity' cases— the non-linear interaction between m = 1 dominant core-resonant modes seems not to adequately explain the (0, 1) mode evolution. Implications for the plasma dynamo mechanisms are accordingly deduced and discussed in comparison with previous findings, and mainly, we conclude that the (0, 1) mode could be an important factor in the torque balance rather than as an active dynamo driver.