Installing new shingles is a major investment for most homeowners so it makes good sense to take steps to protect the integrity.
Replacing a roof jack.
Slide a new roof jack sized to fit your vent pipe over the pipe.
1 remove nails holding down shingles above the pip.
Remove any roofing nails and slide out the shingles.
Find the damaged jack and take measurements of its height and pipe diameter.
Pry up the old jack and remove it by pulling it up over the vent pipe.
Is it necessary to replace roof flashings when replacing shingles.
On the boots if you have metal roof jacks with rubber boot seals on top with many models the rubber seals can be popped off and replaced without removing the metal part and there are also slip over boots that can just nestle down over the existing damaged boot and overlap the top of the jack but contractor would have to look at it and see then go get parts so if using a contractor probably cheaper to just have him bring new ones right off unless quite close to his supply wholesaler.