I am not sure I understand the question. The type of efficiency frontier you describe is about varying weights in an optimal simple rule chosen by the user. That does not make sense in the context of Ramsey or discretionary policy where the policy is unique (but generally cannot be represented as a rule).
A different type of efficiency frontier involves varying the weight on inflation or output in the objective function. That can generally be done with discretionary policy. But in many contexts, there is a unique weighting given by the utility function of the agents. That is for example the case in Gali’s model.