I looked into changing our license from CC BY to CC BY-ND and discussed with our governing body. The obstacle to doing this is that the GitHub repository lists the license as CC BY-ND and the project doesn’t own the copyright to its code (the individual devs do). That means we can’t just change the license to CC BY going forward. So that’s not going to happen.
We didn’t intend to prevent people from reformatting the output. We wanted to stop people providing incomplete or badly modified doc for Stan. But we’re not lawyers and if you want more assurance, I’m afraid you’re going to have to talk to your own lawyers about what rights the CC BY-ND license grants. Sorry about that.