Some of our conversion we had yesterday got me trying to figure out where the break began and what story affected what...got me thinking in a different direction...CDPR should consider breaking down and adding a full 4th Act! or an 'active' epilogue so the player can say his individual good byes, clear out his witcher contracts and side quests remaining...even add a few more as a result of the player's choices.
During this time he would have a chance to visit with his old friends and get right with the world. It would give closure to the story and allow the player to fell like he isn't sprinting to the end of the world!
Now, if they did this, they STILL would need to make a few changes to the current version of Act 2 and Act 3...some very minor issues I think(which means THEY are bind blowingly difficult to actually accomplish). When Geralt makes his choice, there should be some recognition of this down the story-stream.
Kaer Morhen: when Geralt arrives, his love should be there waiting.
If thats Yen, then they have that covered right now! Perfectly even...
If it's Triss though, then they have to add her! A first meeting scene, she could part to her 'chores' and it might make the bed getting destroyed scene make more sense...especially the PISSED off Yen he finds who is NOT up for a discussion(seen the videos on this). The drinking scene takes on an entirely new meaning...and Lambert/Eskal reactions would probably have to be redon. OK!!! That's a major rework BUT...IMO, its a must(and I say that sadly and with grim determination).
Return with Ciri:
Geralt might find a moment to try to soften Ciri on the 'change' his heart has had...maybe, maybe not. When they arrive in the courtyard, Triss should great Geralt first ex-nay the Yen kiss and then they continue on with the prepwork. A scene with Triss or at the very least a cut-scene where she gives him one of her 'looks' or a brief embrace/touch as they pass, with an indifferent looking Yen seeing it...maybe Ciri too. Everything on through the fight even I think fits.
Novigrad 2: The word of Geralt choosing Triss would have preceded Geralt back.
THEY would have a room, Dandelion could tell them. Some others might have a dialog option dropped in...and conversation chains during the bathhouse quest would require some changes. And a scene where the two sneak out to her old 'cozy flat' for a few hours of alone time. I am sure I've 'glossed' over this and it TOO wouldn't be that 'easy' but I am flying by the seat of my pants on this...stream-of-consciousness ya know!
Skelliga 2 and the Boat: to the current end:
Add in a reactive and compassionate Triss (see Novigrad 1 and the rekindling of the flame type stuff if you need suggestions) Recognition from the Clan leaders in Skelliga and a much more involved parting conversation with Triss. Add in a better, more focused talk about where they will go when its all over and I think you have a winner.
In all this, I think the default last half of the game Yen, doesn't need much changing at all. Her sad introspection while Geralt and Ciri are having their moments play right into this...the player can only guess what she is really thinking about.