It is my firm belief that you can take, recreate, modify or otherwise use anything that is publicly available (including .stl, source code art or anything else) if the result of you tinkering is never shared or seen beyond your basement. So if you want to recreate Ryan’s exact designe in painstaking detail go for it, just don’t share it and no one will know or care.
If you do want to share it, the legal definitions seem irrelevant for reasonable and well intentioned members of society(as I belive you are). The reasonable, moral, and just thing to do is simply follow the original creators wishes to the best of your ability. If you think you might step on their toes ask the person that owns/created the work if it is ok. If that person asks you to stop what your doing than stop. I firmly belive legality exist only to keep those who are unreasonable in line. I know I don’t have sources for this argument so take it as you will and it is strictly my personal opinion.
I understand what your saying here but keep in mind what and who you are asking. It’s like walking into a police station and asking under what constitutes stealing. It just doesn’t go over well but none of those officers mean to offend or accuse, there reactions are simply colored by their past experiences. If you have a specific modification in mind bring that idea to us and I bet most will help you with it.
Of you have a specific legal question, mu boss is a licensed Professional Engineer and is only a couple of semesters away from a law degree. I could ask him a specific question and I’m sure he would be happy to answer. But so far I have only seen vague inquiries, but maybe I missed somthing (I do have two small children that keep jumping on my lap distracting me as I read this).
Edit: for an example of how reasonable this group is look here: Idea for pen plotter inspired by and using v1 elements
Not an ill word of copying is spoken despite the original poster’s written intent to copy v1 design XD.
I have said this before, and I will say it again. I belive the core of values of this group are explore, learn, and have fun. If what you are doing aligns with those core values than you should be fine 