You could move/rename the `Extras.rsrc` file in `/System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/HIToolbox.framework/Versions/A/Resources/` and disable Aqua in the very early versions, returning lots of things to a Mac OS X DP2-style Platinum appearance:

https://macosx-dev.omnigroup.narkive.com/WZX5AkMk/extras-rsr...

https://guidebookgallery.org/screenshots/macosxdp2

I also like to use Jagwire's Extras.rsrc on Tiger to get my sweet sweet pinstripes back: https://forums.macrumors.com/threads/jaguar-ui-on-tiger-proj...