Consider the following menu bar item:

Notice that the separator is "--" (between *Messages* and Next Buffer). Is there a way to change the separator? I would like to change it to "======" instead.

The separator is apparently set by menu-bar-separator, which is defined in subr.el:

(defconst menu-bar-separator '("--") "Separator for menus.") 

It appears to be a constant. Does this mean that it is impossible to change the menu bar separator?