It's a bold claim to have expertise in PRoW and to quote a reference which the latter part of the post seems to indicate has either not been read or not properly understood...
Without having any claim of "expertise" (other than having walked them all and having a good knowledge of the parish) I could probably identify 90% or more of the land owners for all designated parish paths.
Anyway, s27(1) clearly dictates that the HA has the power, after consultation, to erect and maintain signs. It does not make any reference to a delegation of the consultation requirement.
s27(5) clearly states that, with the consent of the HA, any other person may erect and maintain signs.
Those 2 parts therefore make perfectly clear what needs to happen - make a list or marked map of the intended location of signs, send it to the HA for their consultation, await their confirmation that landowner consultation has been completed and that any necessary consents obtained, put your signs up.
Let the council officer have their glint in the eye, just give them the list of where you want to put your signs and tell them to crack on and let you know when the consultation is complete. That might just take the shine off it for them....