How to import and link a shapefile of boundary conditions?

I have a regional model that is an expansion of a earlier one. There are slight changes in the node distribution of the mesh, once I had to add the new areas. I want to define boundary conditions in this new model using the boundary conditions of the former one. So I exported the BC in question (head constant along rivers) from the earlier model using the export Data > Current slice (where this BC was defined).  Just to check, I opened the exported file in a SIG and, as expected, it was a point shapefile with all the points along the rivers, as it should be. Aftewards I  imported this file into the panel Maps and linked Z (the height of the terrain) to head constant BC, as in the former model. I mantained the default snap distance (2091,61 m). Then I went into the panel Data, selected head constant BC and when did the procedure to apply the BC along the nodes, I found that it did not defined the BC as it was in the shapefile – that is along the direction of the rivers – but applied it to all the nodes of the area I selected. The way I found to overcome this was to select node by node, for it to apply the BC in the correct nodes. Once this BC has to be applied to the whole river network, so theere is a lot of nodes, I would like to know how can I import the BC shapefile in a way that just the rightful nodes are defined, instead of all the nodes of the model. I have the same exact problem with the Multi-layer wells BC.