Why the fictional Hapes expedition cannot open a third route

Could the Hapes expedition use its force to create a third route into the cluster?

No; the scenario permits only two navigable hyperspace routes.

The proposed third approach is ruled out by the fictional hyperspace constraints. Only two routes into the Hapes Cluster are navigable, so adding another direction of attack is outside the scenario's physical rules. The comparison with crossing the Himalayas illustrates why a route that looks attractive on a map can remain unusable.