1. You say "If you know the load, connect it to node B."
@ How could I know the value of the load?
If the feedback path is rather simple, you can see the load by visual inspection, don´t you?
@ Is the load the input impedance looking into node C ?
Yes, of course! That´s the load disconnected by breakink the loop.
@ How could I measure it?
This makes no sense. Either you derive it by simple inspection (I suppose you know your circuit diagram) or it is a complicated/involved function of frequency.
2. Is the replica of path another accurate solution ?
Yes it is accurate - as far as the load itself is concerned. However, watch the bias condition of the closed loop!
To be on the safe side, use the Middlebrook method which is described elsewhere (google/internet, or also in this forum).