An interesting one, & I don't think you're the only one out of your depth!
I've found this:
http://www.defra.gov.uk/wildlife-countryside/c l/pdf/nercactv5.pdf
Para. 70 seems to be saying that in some circumstances there can be vehicular access on a Restricted Byway - apparently depending on what it was before it became one.
I can't find anything on "long usage rights" - could it be that different terminology is used in the legislation etc.?
I think the only way of answering your query is to find the legislative basis for long usage rights & check what limitations are placed on them. It would certainly seem logical to me that if the right is specific to a particular landowner and his/her particular area of land that it ought not to be transferable to another landowner & different land. But all this depends on how the long usage right arose and what the conditions governing it are.