unfortunately cannot see your pic, however no matter : seen these before. not a bad arrangement...just a bit fiddly
there will be a way to tension downwards slightly on the slider, so that you can release the pin. once the pin is release you can ease the wire off. attach a sufficiently long tail and you now have a conventional halyard
need to take care that the tail is not knotted on to the wire such that it becomes stuck when feeding through, and that the tail is sufficiently strong.
it's not as hard as it sounds...
cheers,