What would happen if you installed non-NO/non-NDO marked tires?

 

See my post #8.

TL;DR - hard to know for sure without Porsche publishing what they did when tuning the N* versions of tires (this won't happen). An educated guess is that you might notice a bit more NVH, or different steering response, but these would be pretty subtle, and if you aren't the "picky" or "enthusiast driver" you may not notice at all.

@BigChief480 I liked your post not b/c I like it, but because I feel your pain. sucks.