Augustine is adamant and explicit that God's Choice to NOT perform the Salvific Miracles in Tyre and Sidon was a matter of His pure prerogative, not limited by any imagined divine "Miracle Bank" from which only a certain number of mighty works might be drawn
No, you are reading what I wrote wrong.
God has ordered the universe in a certain way.
He could also order it in another way.
Ordering it another way precludes the ordering in the first way, its an EITHER/OR logic gate dictated by time and place. Christ cannot be crucified both in Jerusalem and Peking. Lazarus can't be raised from the dead both in Palestine and Anitoch at the same time. Jesus can't sit down at 4 pm by the Sea of Galilee on a Thursday in April in AD 31 to multiply loaves of bread and also do so simultaneously in Armenia.
Christ himself presents the choice of working the miracle in Palestine or Lebanon. Obviously the same miracle cannot be worked in both places simultaneously. They could of course be done sequentially or simultaneously to different subjects, but then the effects would still be different than that fo the choice.
If Christ heals a certain person in Palestine to manifest his glory, He is then constrained from healing the same person again in Lebanon at the same time.
The choice of locations of miracles has consequences in subsequent occurances. "Woe thee, Corozain, woe to thee, Bethsaida: for if in Tyre and Sidon had been wrought the miracles that have been wrought in you, they had long ago done penance in sackcloth and ashes." If done there, consequence X happens there. If done here, consequence Y happens there. EITHER/OR. No possibility of doing the same thing in both places is presented. To put it bluntly YOU MADE THAT UP.
So if Christ converts instead of an Augustine, the wayward son of some illiterate peasant in Gaul, the world is not merely deprived of the conversion of Augustine, but it is deprived of the writings of Augustine which flowed from that conversion and through which God works other conversions. Similarly, if God works miracles in Lebanon instead of Palestine that don't convert the Jews to convert the Syrians, consequences inevitably flow beyond their conversion, because their conversion influences other events.
have left off the remainder of the citation
No, it wasn't and isn't relevant to the point I was addressing.
From this we clearly understand that God could "add something to the present creation"; that is, He could perform Salvific Miracles in Tyre and Sidon and also perform equivalent Miracles in Chorazin and Bethsaida, if He -- of His own pure prerogative -- had so chosen.
I wasn't talking about additions, but choices. Christ can only chose one apostolic leader. He can raise up either Peter or Judas, but not both to the leadership of the twelve. From the single choice of either flow other consequences for the rest of history.
This is entirely true; but it is equally true that God could have chosen to enlighten both, Augustine himself and your other anonymous "wayward son" -- of His own pure prerogative.
Yes He could have, but that wasn't what I was talking about, was it? Why bring it up?
They are not "elect" because God has not created a world in which they are saved, although He could have done so, but perhaps only at the expense of the salvation of others.
In itself, this idea is a direct assault upon the Aseity and Omnipotence of God Himself. It is to bind All-Powerful God with the chains of necessitarian trade-offs -- as the Greek "gods" were bound by the Loom of the Fates, binding the Creator under the creature
Oh baloney OP! God can't just remove people from history and then have no further consequences, because events in time are linked. Take away St. Augustine, and you inevitably must take away his writings and all the influences they have subsequently. We for example, wouldn't be discussing him right now. These influences can be replaced with other influences, but they won't be St. Augustines, and their replacement requries additional choices, while we are just talking about a single choice. The influences from other choices might be of identical influence if God so willed it, but there are many more choices that would dictate they would not be.
The choice of Augustine or an iliterate nobody are not necessitarian, but the consequences are necessitarian. An Augustine influences the world, an illiterate nobody does not. Again, you are introducing elements into the dicussion which are not relevant.
In the first place, I never maintained that Christ was speaking of "doing the same thing in both places at once" -- you made up, me making that up.
In fact, as your own citation of the relevant Scripture indicates, Christ is talking about Miracles which could have "been done sequentially" -- for He says that Tyre and Sidon would have repented "long ago". Thus, salvific Miracles could have been performed in Tyre and Sidon "long ago", which in no way precludes Miracles from being sequentially performed in Chorazin and Bethsaida. Nor is the effect of the miracles claimed to be dependent upon their particular palestinian subjects as you assert; it is the demonstration of the Miracles themselves, upon Tyrians and Sidonians, which is (as a conditional statement of fact) declared to have foreknown salvific effects therein.
Ergo, there is no trade-off in this passage as you claim. Nor, I would add, have you cited anything from either Augustine or Aquinas claiming such a thing -- and I would venture that this is because nothing in the works of either can be found making such a claim, because neither Augustine nor Aquinas asserted anything of the like.