From what I just read about pacstrap, I think so, yeah, but you can control many more things, like for example you can configure KDE to use wobbly windows¹.

But it’s also declarative, rather than just a script.
If you do configure wobbly windows this way, it doesn’t just do a find & replace on the respective KWin config file, but rather it generates the entire KWin config file anew, with all the values you defined in your NixOS config + whatever defaults may be needed.

This has the big advantage that it doesn’t depend on whatever is currently on disk. It will just make your system match your NixOS configuration in any case.
Disadvantage is that any other KWin settings need to live in your NixOS config from now on, too, i.e. you can’t use the graphical settings anymore or they will be overridden on the next nixos-rebuild switch.

Well, and there’s other disadvantages to NixOS, like it not using the standard Unix folder structure (FHS), so some programs have problems with that, and that there’s at least two different ways to do anything, so it’s difficult to find straightforward documentation.

But yeah, if you can push past the pain of learning it and configuring everything initially, it does then work quite nicely.

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¹) Requires Home-Manager and Plasma-Manager, and then this line in your Home-Manager config:

programs.plasma.kwin.effects.wobblyWindows.enable = true;