Main rotor rpm nudges can be effective at the tail end of a procedure, if the aircraft is almost lines up and just a tweek is needed to get the machine aligned with its direction of travel (a very good idea, skids or wheels, since a roll over can be noisy, expensive and painful).
(All directions are consistent with American and British rotor direction, front blades going to the left)
The rpm is a double whammy, increasing the rpm will act like a boost of left pedal and decreasing the rpm will act like right pedal.
Here is why. If the main rotor thrust is held constant as rpm is changed (for example, collective is lowered slightly with up rpm), then a raise in rpm will lower the main rotor torque exactly as the percent rpm increase. This is because the power needed by the rotor is almost constant, and the power is the torque times the rpm. More rpm means that less torque is needed for constant power. An rpm increase makes the current tail rotor pitch setting (which is stuck) produce somewhat more anti-torque, which produces a left nose movement. Also, the rpm increase will further increase the tail rotor thrust for even more left pedal equivilent.
If the main rotor rpm is reduced, the main torque will increase, requiring more anti-torque, and absorbing some of the anti-torque the fixed-pitch tail rotor is putting out. This will cause a right nose swing. As above, the rpm change changes the tail thrust, reducing it in this case and making the right swing even more pronounced.
The tail rotor thrust changes by the square of the rpm change, and the main torque changes linearly.