Some hours before Pickett's Charge Lee tells Pickett to run his men at the highest speed possible across the field to the stone wall. He says he is expecting high casualties but the development of the battle has left him no choice. 'Speed, and only speed, may be your salvation. We will also launch a final artillery barrage as your charge begins and I am asking your men to run right into their own fire, but the effect, of devils swirling up out of the smoke of this mighty bombardment, may just do the trick and break the line. Godspeed."
Would this work, or make things worse?
It's impossible. We are talking about a distance of nearly a mile, mostly uphill, on one of the hottest days of the year. What you have is 10,000 to 12,000 of them down with heat stroke before they get 1/2 way there.
Second, and even more importantly, the scenario ignores the terrain between the Confederate lines and the Union position on Cemetery Ridge...particularly the Emmitsburg Road, which crossed the field at near right angles to the Confederate advance and had a 5 foot high rail fence which ran alongside it. The entire Confederate advance was halted, in OTL, by this fence, which the men had to literally either dismantle or climb over in order to proceed further (a lot of the Confederate casualties occurred while the men were bunched up behind this fence, trying to get past it to continue the advance). If the men get there already exhausted because they have run all the way there in the scorching July heat, mustering the energy to climb over the fence and go on will be well-nigh impossible. In OTL, many of the men did not go beyond that point, but lay down in the field instead of trying to negotiate the obstacle and refused to advance further. Many, many more men will do that in this scenario, and the attack will collapse at this point.
Short version...the Confederate advance never reaches the stone wall at all, but breaks down and is turned back at the Emmitsburg Road. Ironically, probably a lot more of the men survive the attack, because the horrendous casualties suffered as the men charged into blasts of close-range cannister and musket fire as they approached the stone wall don't occur.