It looks like your 1:50 Spritsail Yard is lashed under and to the Bowsprit by a Spritsail sling. Is this sling stationary or is there a lanyard(s) attached to this sling to move it fore and aft along the Bowsprit?
I'm getting my terms from the book "Rigging Period Ship Models" by Lennarth Peterson, page 59. You may have it in your library.
The spritsail yard was usually suspended on a sling rather than a parrel, and it could have a line leading forward, essentially a halliard to haul the yard out on the bowsprit, but this was not usually necessary. Once the optimum location for the yard had been determined, it was fixed there by cleats or something similar. In use, it was not necessary to move the yard on the bowsprit, since the sail was loose-footed with very long sheets leading aft. Bracing the yard tended to pull the ends up as much as aft, and so the yard moved side to side a little, and the lifts could be used to keep it from sagging away from the bowsprit.