You are probably right in your assessment that he is a land nibbler. They often attach 'Property Developer' to their CV as well.
If he applies to register with the LR an alteration to the easement (i.e. right to pass/repass by vehicle as distinct from a right to pass/repass on foot) over land that is registered to you, the first thing that happens is that the LR will write to you to ask for your version of events. Only when they are satisfied that his application is valid will they alter his (and your) land title documents.
So nothing will happen regarding the LR.
What you will have to do, of course, when it comes to selling your house is answer truthfully the standard question that a buyer's solicitor will ask regarding 'have there been any disputes regarding boundaries or access arrangements'. So will he, of course. But that question is unconnected to the LR.