Command: MPEDIT
Select objects: Use an object selection method
Convert Lines and Arcs to polylines? [Yes/No] <Yes>: If no, selection set ignores lines and arcs.
Enter an option [Open/Close/Join/Width/Fit/Spline/Decurve/Ltype gen/eXit] <eXit>: Enter an option

Usage Example:
Draw a circle with overlapping lines and polylines with varying widths; then edit their widths.

Plines with varying widths:

Plines with the same width: