In OSM in the UK, highway=footway already implies bicycle=no, so adding bicycle=dismount has no effect on routing,

None of the objects edited in this changeset are footways in the legal sense, so Highway Code Rule 64 and s. 72 Highway Act 1835 are entirely irrelevant here.

As far as I know, none of these streets are maintainable at public expense, so the degree and modes of permissive access are at the discretion of the landowner. I would rather see a definitive statement on that access from someone with authority to make it.