I'm not sure what your goal is and what your input data looks like, but I think you need the LineCombiner. If the polylines have the same z-value for all vertices you can use the LineCombiner where you combine on the attribute containing the z-value. If needed extract the the z-value with the CoordinateExtractor.

The key is you can use a VertexCreator to insert a point at a specific index in your line, and this can connect the line endpoint to another location, including in the Z dimension.

You first create nodes along the line you want to connect To, and join their x,y,z coordinates as attributes to the line which you want to connect to each node

Will be something like this: This is only connecting one line type to another, you'll need to control whether you add the vertex to the line startpoint or endpoint if the line directions are not consistent.