My cluster has a flickering backlight led and it is driving me nuts. I just found a used cluster. Can I simply swap them? It is identical. Or do I need the dealer to adjust the Ido?

First, not all clusters are the same. IE I had my HVAC controls replaced by the dealer. The new HVAC controls did not work. They also had to replace the cluster to get them to talk together.
Then they had to reprogram the other computers.
Second, a dealer can not reprogram a cluster. The replacement cluster for my rig had to be programmed by CJD Corp engineers with correct mileage, and VIN info. Then it was shipped to the dealer, who did the install and the other computer programming.
I'm real glad the work done to my rig was warrantied, or it would have cost me a fortune!

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07 KA Light Khaki, Manual trany.
2.5" Adjust-A-Strut JBA lift, Euro taillights,
Home made; Front Tilt Hood, Roof Rack, RAM Air, & CAI.
ESP Off Switch
Take a ride on the Trō side!

darn!!! All of this because of a led that cannot be replaced.

Others have changed the LEDs on the cluster to change the colors. I don't see why you couldn't replace yours, if you are careful.

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07 KA Light Khaki, Manual trany.
2.5" Adjust-A-Strut JBA lift, Euro taillights,
Home made; Front Tilt Hood, Roof Rack, RAM Air, & CAI.
ESP Off Switch
Take a ride on the Trō side!