My apologies, I completely mis read that.
I do not believe there is a way to do this outside of sketcher.
Unless you do it manually by trimming lines and adding a new chamfer line.
i did recreate for 3D curve some of the sketcher function like trim using VBA... you can do chamfer also with input like angle/length or length/length ... but this is not OOTB.
Eric N. indocti discant et ament meminisse periti