I am remodeling my second floor. I am re-working all of the pluming system. Is there a 3" flexible tubing that can be used to reconnect to my existing roof vent boots?

Why not tell us exactly what you are trying to do and exactly what problem you are having?

My vent boot is up close to the ridge of my roof. My new vent pipe is at a lower spot at the roof. I am hoping to not have to patch the old boot and cut another hole for a new boot. My roof is sloped less than 45 degrees. So I can't just use 45s. Is it possible to connect the new vent to the old boot with 3" flexible tubing or hose?

Are you saying that the old vent went straight up from the ceiling through the roof and that you move the vent pipe? If so then use a long 90 or sweep, go horizontal over to the old vent location then use another long 90 and go up through the roof , just like the old vent

Or 45s will work just fine too. I am confused about the flexible tubing to adapt to roof jack. So I'm going to say, no. If the new pipe doesn't fit snuggly in the old roof jack, then take the old roof jack off, and install a new one using the same hole.. it can be tricky, but it can be done. You can even install a new roof jack over the old one, but you will most likely have to cut some of the old one off for new one to fit. Lee.