You can only re-assign the first node of a path. In your screenshot, this is correctly done. From the first node on, you count along each node in each master and want it to correspond to the same node in the other master – you do this by keeping the number of nodes identical, so that the (e.g.) fifth node of a path will correspond to the same node in the design of the other master. In your case above, it means that you will either need to take off nodes in your bolder master, or add nodes in your lighter master. Make sure that any node you add corresponds design-wise to the other master. Especially in a design with as many curve segments as yours, adding more nodes will make things messy, I’m afraid. Best to work with as few nodes as possible.
Hope this makes sense.