milo
Jack L. Jones
I think there could be a sector-specific fudge. Ulster agricultural produce gets made to conform to EU regulation (but nothing else), whilst British doesn't, or something along those lines.
That doesn't keep the boarder open. All goods can pass over the boarder, so there would need to be full alignment and membership of the Customs Union to stop boarder posts.
The section in the select committee minutes where they talk about the Poland/Ukraine boarder after Poland joined the EU are interesting on this point.