The tailgate window comes out easily without cutting the seal.
Use a flat-headed screwdriver and wedge-out the inner seal lip. Do this slowly starting from a corner and the window will pop-out. Work from the inside of the car. The window comes out by focring it from the inside of the car. Its diffifult to explain but a 5min job.
To put the window back in use a string, position the window and pull the string. The string will pull-over the inner seal lip. Use washing up liquid to help.