im pretty sure its not notifiable under “part p”, its not a new circuit and as long as its not in a special location then it dont need to be notified.
take the cover off and see where the cables run, hopefully there is 2, if they both go down or up, lift a board (upstairs or down) find cables, cut, identify they are the correct cables with a continuity tester and put a jb on them or crimp and enclose them. leave old cables in wall.
if one goes up and one goes down, get the sds out as its going to get messy!
Not an electrian, but I believe it really has to be a crimp as a JB is not maintainence free, as the floor could later be covered in a way to make it inaccessible. That said, there are now maintainence-free boxes on the market, like Wago.