Yes, good idea to clarify with office either tomorrow or at start of next half term. If you email and ask that everyone knows, it's all in writing and avoids confusion.
But I dont think there's any need to make a complaint about today's conversation. Quite simply, one teacher informally said you could ignore the 1-way system, but the information hasn't been conveyed to all. Sometimes this happens....people have a passing conversation and it remains as this. I do t think you can always assume everyone will know about every conversation that happens between 2 people in an informal way.
And the person you spoke to today simply didn't know. Perhaps you're someone who regularly doesn't like the way someone speaks to you or feels you are being discriminated against or objects to people's tone of speaking to you.....it's hard to tell from this, but from the thread it seems that the issue for you wasn't just about following the one way system but also about the person speaking to you. To be honest, the teachers words all sound quite light-hearted to me and not really something to cause offence.....but we know from MN that people take offence at pretty much everything, and there will always be someone advocating either a 'quiet word' about how they were spoken to or an official complaint.
Accept it for what it was. You'd spoken to someone about a special dispensation for your child. That worked fine for a while as that individual was always the teacher on duty. When someone else appeared today, it became clear that they didn't know what you'd agreed.
It's easily solved without any big drama. It wasn't a conspiracy against your child and it wasn't an attempt to make you feel small. The teacher today just didn't know. The easy solution is a quick word, with a request to let everyone know, or a quick email to the same effect.
The outcome of this is most likely to be that the school simply confirms the agreement you had with the teacher (assuming your child's needs warrant them not going the long way round) and let's all the staff know ....job done! Not a big deal. Of course there is a possibility that they then say that the one -way system needs to apply to all - but that is very unlikely if your child has difficulties which prevent them walking so far - if this is the reply, then you can have a further discussion.
This is such a simple issue and so easily resolved. It hasn't come about become of malice and there's nothing sinister to dwell on. Some simple communication is all that's needed to sort it out.