Plumbing stack vent - code and practicality of re-routing above the roof but under a solar array?

Please respond ONLY if you have some professional expertise on the subject of building codes and plumbing. I install solar electric systems. Installing solar arrays around plumbing stacks on roofs can sometimes be problematic. What are the code requirements and practical issues around re-routing these vents in the 2" to 4" gap between the shingles and the underside of the solar modules? Can I cut the stack short, put a 90 degree elbow on it and run in off to the side? Can I obtain other angled elbows and run it up the roof? I understand that I want to avoid having the vent get blocked by snow or ice.