For offsets and ranges you'll need to isolate that section of the animation, perform the scripted task, then add it back in.

Save the required pose to the pose library using the desired frame range, save scene.
New scene, new figure, apply the saved pose, apply the script, save new pose to the library.
Reload the original scene and apply the new pose at the desired frame. First drag frames to the right of the insertion point to the right to give space for the inserted pose. Apply spline breaks as required.

IK's on/off will make no difference.