OK, how about the exchange happening without a war? IIRC, in OTL some kind of a swap happened (don’t remember if this was during EI or CII reign) with something going to Oldenburg and Denmark getting the Holstein/Schleswig and all this did not require a major war or any war at all. I understand that you guys are extremely blood thirsty but is a war really prerequisite for coming to a consensus?
So the basic question is: are the Danish and Swedish rulers so bent on a quarrel over small pieces of land (and, as I understand, even one which none of them possesses, quarrel over Holstein) that they are going to ignore a possibility of the extremely profitable (as in for pretty much nothing) arrangement?
OTL, Denmark got Holstein 1721 as the Duke a vassal to the King of Denmark, although the Duchy was still nominally part of the Holy Roman Empire (the normal mess of non-HRE monarchs with posessions inside the HRE). Holstein-Gottorp independent and allied to Sweden is "a pistol in the Danish realm's back" as was expressed by a Danish diplomat. Combined with the close-fought Scanian war, the revanchism for Scania, I have a hard time seeing a reconcilation between Denmark and Sweden at this time. They have been existential threats to each other, are each others arch-enemies and have fought more wars against each other than England and France.
Karl is unlikely to sell out his nephew Karl Fredrik (it would not be honourable), and the strategic position Sweden holds at the moment - with Holstein-Gottorp and its gaurantee by the Dutch and British through the Altona convention is combined with the alliance with Russia makes Sweden's current position quite good, and they have no real reason to seek change.
As for Denmark, one of the few things they don't lack is coin, since they still control the Sound dues. They do seethe with revanchism, and the idea that thy CAN take Sweden, if no grand power intervenes on Sweden's side (and Russia is not considered a grand power jut yet, just a strong regional power - their ability to project power against Danish interests is quite limited to nil).
It is about prestige, revanchism and national ideas. While you and me, with hindsight, may think it would be a much better idea for Denmark to seek a compromise and make money and secure its future in northern Germany, the contemporary Danish elite would not see it that way. 1658 and 1660 Sweden tried to end Denmark as a sovereign nation, this figures quite actively in the minds of the Danish elite.
The Danes do not have enemies in Germany at the moment (apart from Holstein-Gottorp, but that is only because it is allied to Sweden), quite the opposite - Hannover and Prussia are potential allies against Sweden.
OTL, the Danish army returned from the War of Spanish Succession experienced and victorious. If they suffer catastrophic defeats, the Danes might realise that their ability to wage a war of revanchism does not exist, but OTL and ITTL, they thought they could get it back, an they would try, for prestige and getting what they considered the eastern half of their realm back.
Like Germany 1933, they needed another defeat to realise revanchism is not a good idea.