With GPUs you can do things like dump its BIOS, alter the identification string, and then re-flash the card.

I’ve modified a lot of GPU BIOSes to tweak GPU and memory clock timings or enable Mac support.

CPUs aren’t that easy to modify. I am not aware of any consumer tools that can simply re-write CPU’s internal code.

Regardless, the first time you run a benchmark and it shows that your CPU is really X and not Y, you will know something is wrong.