This code snippet illustrate the core of generating actions in PlayMaker programmatically. It is only dealing DebugLog action. Other actions that have event as the fields may need different approach. Besides, the code is not cleaned up yet.

CreatePlayMakerState.cs

// Just a method of the class
void TestAddProcess()
{
    if (_theGameObject != null)
    {
        _theGameObject.AddComponent<PlayMakerFSM>();
        PlayMakerFSM pmFsm = _theGameObject.GetComponent<PlayMakerFSM>();
        if (pmFsm != null)
        {
            // Need to select fsm first
            FsmEditor.SelectFsm(pmFsm.Fsm);

            // Add states
            FsmState fsmState1 = FsmEditor.Builder.AddState(new Vector2(200.0f, 200.0f));
            FsmState fsmState2 = FsmEditor.Builder.AddState(new Vector2(200.0f, 250.0f));
            FsmState fsmState3 = FsmEditor.Builder.AddState(new Vector2(200.0f, 300.0f));
            FsmState fsmState4 = FsmEditor.Builder.AddState(new Vector2(200.0f, 350.0f));

            fsmState1.Name = "Yesterady";
            fsmState2.Name = "Today";
            fsmState3.Name = "Tomorrow";
            fsmState4.Name = "Forever";

            // Add action
            Type debugLogType = typeof(HutongGames.PlayMaker.Actions.DebugLog);
            FsmStateAction fsmStateAction1 = FsmEditor.Builder.AddAction(fsmState1, debugLogType);

            FieldInfo[] fieldInfos = ActionData.GetFields(debugLogType);
            foreach (FieldInfo fieldInfo in fieldInfos)
            {
                if (fieldInfo.Name == "text")
                {
                    if (ReflectionUtils.CanSetMemberValue(fieldInfo))
                    {
                        // Change value
                        ReflectionUtils.SetMemberValue(fieldInfo, fsmStateAction1, (FsmString)"Strange string");
                    }
                }
            }

            List<FsmStateAction> actionList = new List<FsmStateAction>();
            actionList.Add(fsmStateAction1);
            
            // The key setp. Adjusted state action(s) have to be set back using svae.
            fsmState1.ActionData.SaveActions(actionList.ToArray());

            // Add transition
            FsmEvent fsmEvent = new FsmEvent("FINISHED");
            FsmTransition fsmTransition = FsmEditor.Builder.AddTransition(fsmState1, fsmState2.Name, fsmEvent);

            // Set start state
            pmFsm.Fsm.StartState = fsmState1.Name;
        }
    }
}