I've tried to use the QUESTION.stepinfo object, but I only get null when I try to access it.
Do I have to enable this somewhere that it is actually filled with data?
Certainly I hope nothing breaks. I try always to maintain forward compatibility. No-one has reported any issues to me. The only two things that come to mind are:
Regarding the practicalities of upgrading CoderRunner, and knowing if your questions all still work.
For every question you create, you should fill in the 'Answer' field, which should be a response that gets graded correct (and this will be checked if you keep the 'Validate on save' option switched on.
If you do this, then you can go to the admin screen for CodeRunner, and then to the 'bulk tester script', (or just go straight to the URL .../question/type/coderunner/bulktestindex.php.
That will test each of your questions by trying to grade the given 'Answer' and checking that gets 100%. Doing that is a pretty good confidence check that all your questions still work.