I have never seen one written down, but it would not be any different than the one that other scientists follow. I can imagine that paramount in such a code would be the injunction not to knowingly falsify data. There is no greater sin in science than to manufacture data to fit your expectations, or to knowingly bias a 'calibration' process to favor a particular outcome. Fortunately, it is professional suicide to do this because once someone else cannot reproduce your results, your career is over. Of course there are situations where particular data cannot be confirmed because the event or phenomenon 'only did it once', but allowance is made for this by other astronomers. That's why there is so much excitement about 'gamma ray bursts' because they never seem to reoccur, although over 1000 have now been detected.
What applies to data also applies to developing theories of how some phenomenon operates, however, even the best mathematicians can make errors in their formulations. That's why every research paper is evaluated in a peer review process before publication, and why every author distributes their manuscripts to colleagues to catch typos and obvious errors in concept or calculation. Even Einstein was called on the carpet by the Russian mathematician Friedman for having divided by a quantity that under certain circumstances can be zero, thus invalidating the calculation...or at least that's the story I recall.
Beyond these injunctions to honor the integrity of data and mathematics regardless of where they take you, I can not think of too many other rules that apply specifically to astronomy, that do not also apply to all other careers.