One of the checklist items for an on-topic question is:
Do I want feedback about any or all facets of the code?
I have considered posting old code to CR which I think would spur useful discussion that would be relevant to future visitors of the site. StackOverflow, for example, has many highly rated questions which were not asked because the questioner personally needed the answer.
In regards to the quoted rule of thumb: I would not actually be using this feedback to modify the original code, either because it is not in use anymore, or because its usefulness is dominated by its longstanding correct execution, which is not worth risking for stylistic reasons.