1) save the file as a new file name, this way any changes you make do not effect the original file.
2) Extract edges for the top surface of the blade.
3) Create a UCS that aligns to the geometry
4) create an offset profile of the surface boundary for how much you want to extend the cut
5) use that wire frame to create a surface
6) select the new surface as your drive surface for your toolpath
Bottom line BobCAD's toolpath is being driven by the selected geometry. Make adjustments to the geometry changes where the toolpath with go.
If you would like to see a step by step example of this, send me your file and join the BobCAD After Dark Facebook Group, I'll do a live video on your file tomorrow. ( shown in V33, but much of the workflow will carry over to V27 )
https://www.facebook.com/groups/bobcadafterdark