score:5
Probably not.
Posey's brigade had only 1300 men. Wright was advancing into the gap left when the III corps under Sickles advanced out to the Peach Orchard and Emmitsburg Road. Odds are that Posey would have been advancing into the II, I, and XI corps units on the hill that the next day would repel Pickett's Charge. Posey would have been exposed to flanking fire from the batteries and might not have gotten as far as Wright, who had some 'cover' due to his breaking the forward lines and having Union troops in the way.
Another consideration is that VI corps had arrived and was being deployed to plug the gap, and units from XII corps were also rushing to the area. The Union was about to get very strong in that area, which is why Wright retired. Posey's men would not likely change the balance all that much.