To copy all (visual) properties from a shape A to a shape B (both in the same editor window):
0) assuming nothing selected at this point
1) select A (single mouse click)
2) find B in the 'Current Elements' palette section in the Palette
3) open the context menu of B (mouse right-click)
4) choose 'Apply' from the context menu
(If you hover long enough over 'Apply', the tooltip will appear.)
See also this answer:
http://yed.yworks.com/support/qa/246
(If A and B are in different editor windows, you could temporarily copy B to A's editor window.)