does microsoft change serial and not replace the console?

what was the repair cost? was it the 115.00 flat fee that i've heard of?

Hi there Noah welcome to the community forum! Christopher here, an Xbox fan just like you and has been on Xbox for years already. I would really love to make your day by helping you out. That means they changed the device!

every service inspects their products on return before replacing the unit

if the console serial number does not match the order they will not replace it

they must see the label therefore they must inspect the unit

If your console does not provide an image, on different devices and with different cables and you have not mistaken the outputs of the console, it should be replaced. To check, if they replaced the console best is to write down the serial number.
Here in Germany you will get your money back after the 3rd failed repair attempt. Perhaps this is why the console is almost always replaced.

Your warranty should be the remaining warranty time of your original console, or 95 days, whichever is longer.

I'm not 100% on this, but my best guess is that the console is the same with replaced hardware. The serial number is the same, and maybe they changed the console ID as a way to verify that it's a console that's been serviced/received new hardware.

I'm just guessing here, though. I remember when my 360 was replaced I was sent a new console and I'm pretty sure it had a new serial number.