The only way I have found to clear this history is to open the file in Est 2015 or Cadmep 2015, save it , then open back up in Est 2017 or Cadmep 2017. Have not tested on the Cad side but it works on the Est side.

I also don't like the elevation history being stored for the whole duration of the project file. I can see where it might come in handy for constant elevations in some instances but there should be a way to clear the elevation history just like in resetting the drawings numbers or sections. Please change this in the Fabrication 2017 products and future versions so we can manage the elevation history of runs and terminals on the entry tab for designline.