The Make Overlap Contour > Make Overlap command analyzes your selection within a glyph, and tries to detach glyph stems or other outline elements from one another. It is similar to the Create Overlaps operation, but it works on the selected nodes and contours, rather than on one or more selected glyphs.
After stems or outline elements are detached, you can easily move them to achieve better glyph shape. When finished, use the Contour > Remove Overlap command to merge contours back or leave them as is. FontLab will merge overlapping contours on export if needed. See also the Remove Overlap page.