Research code is production code and should be treated as such. It doesn't matter if requirements change quickly, you still need to treat it like it's production code... you document, test, and deploy it. And you should include the ability to adapt the code to flexible requirements in your initial design.

Just because you may only use the program once doesn't mean that you can neglect good software engineering practices.

I run into bad code all of the time (some of it mine!) in our research, and it's very frustrating.