[igouy]

afaik Smalltalk implementations usually provide step backwards but don't "run backwards".

"The stack of (framed) execution contexts gives a history of the computation so far. You can select any frame, view instance values in the receiver, view the arguments and method variables at that point."

So step backwards, modify a method, step backwards before that method send, and resume execution with the modified method. (Note: resume rather than restart, so the modified method has the preserved context unless we manually edit that context.)