What @how said! 
I've been to two Zen centers and two Zen sitting groups. All of them had chairs and benches and your preference was not even a matter of discussion, you just picked up the one you wanted.
I too (I believe) screwed up my right knee trying to sit in lotus style. The "need" to do it that way was just in my head.
So be clear, is it semantics linguistically for you or is it guidance vs commands/rules?
Edit - so I re-read your OP rigidly again. Your question above to me seems like a loaded gun. Hindus believe in Atman and a creator, Buddhism teaches anatman and no creator. My personal opinion - AGAIN - is that the Buddha himself has put the 5 precepts in place for a very good reason (after all, he is awake yes?). So if I am following his teachings seriously, I will take the Precepts seriously - as I previously stated. It seems like a logical progression for anyone seriously journeying this path. Otherwise, there are plenty of other ones to choose 
For every party there's a party pooper.
Perhaps even folks who have taken and have tried to live by the 16 precepts for the last 49 years, think that it's the actualization of such vows, and not a perfect description of them, that's important.
Whether directed externally or internally, only in this one fleeting moment, can you become a manifestation of those vows or not. With the next nanosecond, another chance to renew such precepts is offered endlessly again....& again.
There may well be as many different motivations to follow one's vows or precepts or commandments as there are people.
Divide off those motivations and categorize them according to your chosen values if you must
but remember that even with such vows whenever they are clung to, rejected or deliberately ignored, they inevitably bring to fruition, the seeds of our own suffering.
how
Are precepts commandments?
Is Buddhism Christianity?
In my view the difference between precepts and commandments follows from the differences in how we view the religion/philosophy: In Christianity, there is a god (or maybe three), and he is authoritarian and issues commandments. Buddha specifically said he isn't a god, he is awake.
Do all Christians follow all the commandments (can they even name them all without looking them up)? Do all Buddhists follow all the precepts? So, as a practical matter, is there actually a difference between the two?
Hey vinlyn!
To me it seems pretty clear that they are meant as trainings to help us develop spiritually. If the purpose of the teachings is enlightenment then to that end its important for us to learn and grow. Following rules doesn't really get us there.
In terms of karma and multiple lives. Strictly following them would help ensure better future karma. But again, in terms of spiritual development, we need to gain wisdom and understanding so its important to understand the way cause and effect works regarding our actions around the precepts rather than following rules. Which isn't developing wisdom.
person
Few things in an active Zen monastery, temple or Center speak more clearly about a lineage's unhealthy adherence to rite and ritual than a meditation hall that doesn't make allowances for the varying physical limitations of its practitioners.
Every temple and monastery that I've attended has made benches & chairs available, without any discernable muss or fuss, for anyone wishing one.
Even Japanese temples where the meditation, lectures, eating & sleeping were all done on the same spot on formally raised tans to sit on in meditation halls, had a part of that tan that could be removed, for anyone who wanted it, to allow a chair like sitting posture.
How they respond to your question of adaptation to a physical limitation is a good meter of measurement for how compassion, empathy, tenderness & sympathy is approached in their Dharma.
how
Stories are Mara's playground. My story, history, your story... But that is what makes life interesting, no? Netflix, HBO, Disney, Discovery, History Channel
Just something to give meaning to (distraction from?) reality.
Then Mara the Evil One, wanting to arouse fear, horripilation, & terror in her, wanting to make her fall away from concentration, approached her & addressed her in verse:
By whom was this living being created?
Where is the living being's maker?
Where has the living being originated?
Where does the living being
cease?https://www.accesstoinsight.org/tipitaka/sn/sn05/sn05.010.than.html
"This is how he attends inappropriately: 'Was I in the past? Was I not in the past? What was I in the past? How was I in the past? Having been what, what was I in the past? Shall I be in the future? Shall I not be in the future? What shall I be in the future? How shall I be in the future? Having been what, what shall I be in the future?' Or else he is inwardly perplexed about the immediate present: 'Am I? Am I not? What am I? How am I? Where has this being come from? Where is it bound?'
https://www.accesstoinsight.org/tipitaka/mn/mn.002.than.html
Hi Vinlyn!
For me all the precepts make kind of sense, like "why wouldn't you follow them?" though the fifth precept was always a bit of a conflictive one. Ah Mary Jane...my love...sweet thick smoke... ehm... yes, back to the precepts being commandments or not.
I would define them as "great suggestions", in line with what you said as "guidance", not biblical commandments. In another thread I posted here I shared Ajahn Jayasaro's view on the 5 Precepts. In a nutshell: they help us to avoid the negative effects of bad kamma which is detrimental to our spiritual growth.
Kotishka
Welcome back @vinlyn
I'm in the guidance camp with a big dollop of Ehipassiko (seeing for myself]) thrown in for good measure...
Commandment = Something that must be obeyed ( like for example an order from a god )
Guidance =Advice or information aimed at resolving a problem or difficulty, especially as given by someone in authority. ( like for example the Buddha)
Ehipassiko = Here's the DIY guide...knock yourself out...
Shoshin1