Install the .rwp as instructed then ignore the procedure to install the .bat file.

Go to Assets\Oovee\BRClass156Pack01\Particles and copy the file named ParticleGizmo.GeoPcDx and paste it into Assets\Oovee\BRClass156Pack01\RailVehicles\Diesel\BRClass156\Northern_rf\Particles

Go to Assets\Oovee\BRClass156Pack01\RailVehicles\Diesel\BRClass156\Default\PaxView and copy the file named Class156_PaxView.GeoPcDx and paste it into Assets\Oovee\BRClass156Pack01\RailVehicles\Diesel\BRClass156\Northern_rf\PaxView

Go to Assets\Oovee\BRClass156Pack01\RailVehicles\Diesel\BRClass156\One and copy the two files named Class156_DMS.GeoPcDx and Class156_DMSL.GeoPcDx and paste them both into Assets\Oovee\BRClass156Pack01\RailVehicles\Diesel\BRClass156\Northern_rf

Go to Assets\Oovee and delete the unused .bat file