whack
v.
According to arch-hacker James Gosling (designer of NeWS, GOSMACS and Java), to “…modify a program with no idea whatsoever how it works.”
(See whacker.)
It is actually possible to do this in nontrivial circumstances if the change is small and well-defined and you are very good at glarking things from context.
As a trivial example, it is relatively easy to change all stderr
writes to stdout
writes in a piece of C filter code which remains otherwise mysterious.