Moddable they are.
Also, you shouldnt look at the nodes as cot:s but rather an areas where trade can flow through/be generated in and where you can use your influence to for greater control and profit. The actual province where the symbol of the node happens to be is not really important, if you where to build up Crete for example as a great trading port then that might be the most important trading location in the 'Alexandria' trade area.
So the Node is a representation of all the trade that is generated, incoming and outgoing of the area the Node is placed in. It wouldnt matter if the Node of Alexandria was in Alexandria or in Cyprus/Crete or any other province in the area. If you have presence in a Node area you can send merchants to that Node. The Node also show the amount of provinces every country holds in the Node area aswell as if that country is protecting trade with their ships, if they have opend an office and how much gold they generate from said office (or extracting to another node area). Quite clever