That is obviously true. I not only think that they still used AL-31, but didn't bother to change the nozzles (make it jagged). The last photo you posted is clear enough for us to see that.
This is also one of the more likely reasons the intakes were revised as well, to optimize airflows into the AL-31, in order for it to max out the J-20 airframe for high AOA and higher mach numbers, possibly even supercruise, allowing them to "PUSH" this airframe closer to its maximum performance potential. Increasing thermal efficiencies in the "hot-section", as well as reducing drag in and around the old inlet section, and cleaning the inlets up aerodynamically allow them to kill three birds with one stone, as well as reducing possible buffeting tendencies. Its all looking more like they are serious going forward with this basic airframe, and that their initial flight testing has yielded a significant amount of cogent data.