No, reissue it not required unless transit is changed to stopover (or vv.). Similarly revalidation is allowed for a routing change provided that the origin/destination is the same. So for example JFK-HKG-DPS changed to JFK-LAX-HKG-DPS is a revalidation as long as there are no stopovers; even changing to HKG-LAX-SYD-DPS is a revalidation provided that the fare allows it. Most fares do have a lower fee for revalidation than reissue, also the fuel surcharge etc. is not recalculated (in fact there is never an ADDCOL for revalidation). You really want to revalidate whenever possible rather than reissue, unless you are reissuing to a lower fare basis.