One caveat though is if the OP has checked bags. My experience is if there is a checked bag, the system will not allow an SDC through the automated tools like the app. I've tested this where the record was split with my wife and I, and the only difference was the checked bag was in my name - wife was able to SDC the second leg on the app while I couldn't.

I have had an agent do it with a checked bag, but this was domestic connection where PPBM is not required (and our bag did end up traveling on the original connection). For international, it may be immensely more difficult to find an agent who will do this because the bag has to travel on the same flight so there is a whole other set of circumstances involved. It's not that it can't be done, but it is a different/more difficult process, and some agents don't even take VDBs if they have bags checked because of this, much less a completely voluntary change.

YMMV, as always, of course.

As for same fare class, note that it does not have to be available - though you'd have to pay the SDC fee plus any fare difference for a higher fare class. And only an agent can do this, IME. I would think this will also be a potential issue during the holiday season where flights are often full, but again, YMMV.