The first of four dress rehearsals is at hand for the 2012 Green Bay Packers as they open the Pre-Season against the Chargers in San Diego.  At least 16 players will take a pass because of injuries and even more than usual for an exhibition opener, there will be some unusual personel combinations on the field.  Mike McCarthy's first order of business is to get quarterback Graham Harrell as many snaps as possible over the next month.   Aaron Rodgers may work a series, maybe none at all and it's vital Harrell is prepared to play if something happens when the games count.  Watch how the defense gets the ball on the ground.  Tackling or the lack thereof, was a sore spot all year in 2011.  I'd expect a more energetic effort at Quallcom Stadium.  While there are plenty of back-up jobs available, there appears to be only one starting position left open, cornerback opposite Tramon Williams.  Second year pro Davon House may have a slight edge right now, but veterans Jarrett Bush and Sam Shields are in the mix, as is draft choice Casey Hayward.  Good and bad plays are both easy to spot in the secondary.   It's a big night for Herb Taylor.  He's getting the start for the concussed Marshall Newhouse at left tackle.  Taylor hasn't appeared in an NFL game for a couple of years after starting his career in Kansas City.  The Packers say they like the young, inexperienced backup offensive linemen in camp, but they still went out and signed 10 year veteran Reggie Wells on Wednesday.  He started 90 games for the Arizona Cardinals over his career, stopped in Philly and appeared in five games with Carolina last year.  It's an indication they may not be so satisfied with the backups after all.  The Pack also signed wide receiver Andy Brewer, a first year player out of Northwestern.  After a go in the UFL, Brewer tried out but was cut by the Eagles this summer.   To make room,  the team waived guard Jaymes Brooks and put tackle Mike McCabe on season ending injured reserve with a hip injury.  I'll have a review of the Packers-Chargers game posted after the final gun, along with some quotes from Quallcom.