I need some help finding a better way to implement my game mechanic which heavily involves tiles

[potent heath]

Ahoy there. So I am making a game with a mechanic where you can swap tiles to the other side of the screen. There's a video of an early build down below to let you understand the idea better.
What I'm doing right now is using a TileMap where each tile is one pixel. Then I get every tile between the start of the dragging position and where the mouse dragging ends. After that, I get the cell value of the tiles, and set the value to whatever the negative y tiles' cell value is. Obviously though, this is less than ideal as having tiles be single pixels causes performance issues with large platforms and it's a big pain to make any sort of platform. So I need a better way to do this. I have very little idea though...

[dire swan]

This looks tricky, and will probably need specialised mesh generation in which you do 2D boolean operations to copy parts of textured tile quads into new meshes.

You might not be able to use tilemaps for this.