Can a sliding genioplasty or similar procedure be done without adding vertical projection?

Most patients who have the appearance of a long chin are usually over-projected and require reduction genioplasty. Patients who have a recessed chin tend to appear short and the advancement gives the appearance of a longer lower face when viewed from the front. Photographs and/or x-rays would be beneficial to help with making recommendations. 

The sliding genioplasty is done by making an oblique cut in the chin and allowing the lower chin segment to move forward and then maintaining it's location with a small plate and screws. This normally reduces the vertical height as it increases the forward projection. depending on the angle of the cut the vertical height could be maintained. Your surgeon can answer this best as he has seen you X rays. Chin implants could add forward projection without adding vertical height and I think this is a much simpler operation. 

Yes, the cuts in the bone can angled a way that a sliding genioplasty can either add height, reduce height, or maintain it.  If your age is the only reason your are writing off a chin implant I would encourage you to keep an open mind.  A well placed implant will easily last a lifetime, and at the same time they are easier to reverse or change than a genioplasty.  The most common reason I recommend a genioplasty is to make unique changes that there isn't a perfect implant for.  -Dr. Rolfes