I would like a mod setting, or a fork, or something that lets me apply this to Biters Only, or Nauvis Enemies Only. Is this possible?

Reasoning:
The scaling on biters is IMO much more fun than the scaling on pentapods and demolishers. Biters get tougher and deadlier so I have to fortify my defenses more than in the basegame, and the biters stay an interesting threat that I can kill but they damage my walls a bit.
But: Pentapods getting much more Range on their attacks from Quality means they can outrange rocket turrets (at Legendary Small Strafer, Epic Medium or Rare Big) and tesla turrets, so static defense stops working because it can't shoot back! I can try to make quality turrets too so they get more range, but quality ingredients are more limited and unreliable while pentapods spawn without limit, and even a Rare Rocket Turret still has less range than a Legendary Big Strafer.
Demolishers are already huge chunks of HP that I don't "fight" in a sense, I just put up huge turret blocks for them to die on, and if one of them had extra HP then I would simply add another row of turrets. Quality doesn't make them interesting.

Thanks for the feedback — I think your reasoning is completely valid.

Yes, this is possible.

As some background, I’ve confirmed through test play that this mod can be cleared on its own.
I’ve also tested it with BreedingDemolisher and TrueFulgoraConqueror enabled, and verified that it’s still possible to finish on "Death World Marathon" settings.
That said, it is honestly quite challenging, and I don’t expect this level of difficulty to appeal to everyone.

On the other hand, I’m also aware that there are players who find the extreme scaling of high-quality pentapods and demolishers fun and welcome.
In fact, one of my other mods was created in response to feedback from players who wanted to fight high-quality demolishers repeatedly.

As a possible solution, I can add an option to this mod that allows limiting which enemy types are affected by Quality
(e.g. biters only / Nauvis enemies only / all enemies).

Would this direction be preferable for you?

Oops, my mistake — this mod doesn’t change demolishers at all.

As a possible solution, I can add an option to this mod that allows limiting which enemy types are affected by Quality
(e.g. biters only / Nauvis enemies only / all enemies).

Would this direction be preferable for you?

That would be a good option. Yes please, and thank you!

I’ve added a settings page that lets you enable or disable Quality replacement by enemy group (Default, Space Age, and supported enemy mods).
Hope this works well for you — thanks for the suggestion!