You can perform operations on a variable selected in the Variables area by the standard action commands which are available in the Variables menu or from the contextual menu on the variables list itself. For more details about these commands, see Performing operations on selected objects.
Variables > Set...
to set the value of a variable selected in the Variables area. A dialog prompts you to enter a form which is evaluated to yield the new value for the variable. The Common Lisp variable
is bound to the current value of the variable in the frame.