From what I have seen in all my years here, is that there has to be some sort of a loss in order for the wayward spouse to turn around in any kind of way...
And any kind of ploy, or act to do so...will backfire...
I am talking of genuine loss, in order for anything to change....
And more often than not, because the loss is real, the LBS holds the key to all of this....
In my humble opinion, your Ex has never lost you, and therefore has no reason to ever seek you out, other than to get her way with your parenting.....
If it were me, my response to her latest, would be...
I think it best, if we stick to our current schedule, so that we do not to confuse our Son any further.