When elevating a line to a surface the vertical elevations in the horizontal field are removed or nulled, and vertical is then fielded in the vertical tab of edit line string.(?) Which is excellent, I personally prefer working with elevations of a line in this format. Below is a line that requires elevating to a surface modification.
I have now used the Change Elevation command to elevate that line. Where the slope of the line does not change it will not populate a new VPI at every triangle. This limits my ability to control where triangles are created once these lines are used to generate a surface model.
All of this is extremely important to me because I use this method to adjust my 3D line work which is going to be used to generate a site model out of multiple corridors and intersections.