My mobile home has a vent pipe under the bathroom sink which goes straight up. I want to replace the sink but the vent pipe is in the way. Can I replace this straight vertical pipe with an s pipe so it is out of the way of the new sink?

if i'm understanding you correctly, you can offset the vent pipe using 45 degree bends but no greater until you reach 6 inches above the countertop. at that height 90's are fine.

if the occasion warrants it, I have used 60's instead of 45's with no problems.

If the vent pipe is exposed in the cabinet does mean you have an aav under the cabinet or an exposed vent pipe that goes to or through the ceiling

Packy I have a 2" vent pipe with a 90 offset, and the problem is the one time it needs snaking, the drain cleaning tech cannot get a full size 2" head through the offset, then he tried a 1.5" and still no go, finally used a much smaller head like 7/8 or 3/4 and got passed it. I wonder if it's a skill/experience thing or if the installation was bad or an offset will make it hard to navigate.

cleanouts are required by code.
with the exception of being able to remove a fixture to access a clog.
if an installer is intending for a roof vent to be an access point then long sweep 90's should be used.