I need some help, I'm working on a commercial project and need to resize elements by a few inches. After changing the size of the models, it is necessary to correct the UV as seamless textures are used and the rotation of the islands should remain as it is, but the blender have only unwrap that ruin texel density and rotation of islands. It is necessary to correct more than 200 models and each time manually rotate and changing texel density of the islands far too long. I know that in Maya there is an unfold operation, it re unwrap selected islands but leaves the texel and rotation the same, is there any addon for blender that would add such functionality, or maybe there are some other tips? Or just switch to maya for that specific task?
I've had the same problem as you and found a solution for it, hope it works for you:
Select the UV islands' bounds. I used an addon called "textools" for it.
Open UV > Pin in the menu OR press P to pin the vertices so it's kept on place.
Then unwrap it.
There might be some issues for some islands you can simply undo and hide the islands that had issues and re-unwrap again.