With any decent scripting language (such as Perl, Tcl, Python, Ruby, or Lisp), my script would be trivial to write. Granted, such tinkerability would probably require architectural changes to the browser. It would have to be divided into components with clear interfaces, hooks would have to be added, internal data structures would have to be modified so they make sense in terms of the external interface, and so forth. That sounds like a big deal, but it's not so hard if you think about tinkerability from the start. And there are many ancillary benefits such as lower maintenance costs, contributions from a vibrant user community, and more readily testable products.
A world with tinkerable software would have as many magazines about software product improvement as about home improvement or hot rods. And just as we can improve where we live and what we drive, we could improve the software we use. I'd like to see that world.
What are your thoughts? What kind of tinkerability would you dream up?