In postscript, the bind operator replaces executable operator names in the top-most stack element by their values in the current dictionary stack. This can be used to redefine a function in terms of its old meaning, effectively advising it. If, for example, I want to double the width of all lines in an eps, I can simply wrap it as follows.
%!
gsave
/setlinewidth {2 mul setlinewidth} bind def
1 setlinewidth
% ...
grestore