Having done numerous secondary jaw angle reconstructions after initial jaw angle reductions, the key question is the style and size of the jaw angle implants used. In some cases, custom jaw angle implants are ideally needed. While there is more scar tissue due to the initial surgery, the risk of infection is no higher than with the placement of jaw angle implants when no prior surgery has been performed. There is no reason whatsoever to use an external approach neck incision approach for this type of surgery. Restoration of the bony jaw angles will help pick up any loose sagging tissue due to the increased skeletal support. This is particularly true when the jaw angle restoration has a significant vertical component to it.
The access intraoral does have a higher risk of infection as all oral procedures do.but the risk is not unreasonable given the avoidance of facial scars. The risk should not be greater given previous surgery. The skin contours will change but the magnitude will vary with the implants and any loss of fullness from the first surgery.