I'm not sure about question #1. I'm sure there is a lisp out there that
someone has created that could draw a pline etc. from one desc to
another desc with the same block/point then you could
create a breakline from that line.
#2 Here is an explanation from the help file;
Breaklines force surface triangulation along the breakline preventing triangulation across the breakline.
Breaklines are critical to creating an accurate surface model because it is the interpolation of the data, not only the data itself, that determines the shape of the model.
NoteYou can add breaklines only to TIN surfaces.
Hope that helps!