Yea, I keep thinking of why I’d need to do this for PETG alone and can’t come up with a reason. I have adjusted my Z offset on my x1-c for a specific plate before, but never for specific filaments. And that’s only because I use the textured plate setting for a not so textured plate. You might have an issue with your machine if this is necessary.
The only time I’ve ran into something similar was with my QIDI plus 4 before I sold it. I had to set different Z offsets for different filaments. Basically the same thing you’re doing. But this wasn’t a filament problem, it was a machine problem. The peizo sensors for the bed would fail at higher temperatures. It’s a well known thing for the plus 4.