MacOS – Safari print preview set scale to 95% as default

I would use Terminal commands slightly different from @Bart's above, although those work just fine.

To disable Preview's default print scaling:

defaults write com.apple.Preview PVImagePrintingScaleMode -bool false

To restore Preview's default print scaling:

defaults write com.apple.Preview PVImagePrintingScaleMode -bool true 

That way, the default stays in Preview's plist, so I don't need some external reminder about that default if I'm poking into it next year when I've forgotten I did this.

Incidentally, the first time I started up Preview after disabling its print scaling, it seemed to hang on launch, so I force-quit and then tried again and it was fine.

Hmm. Tried to edit to make the code lines show...

In the print dialog you should save a new preset. Below you can find the steps to do so.

1. Open the Print dialog. It will look something like this:
2. Check the Two-Sided box.
3. Go to the Presets drop down list and click Save As...
4. Type a name for the preset in the dialog and choose if you want this preset available for all your installed printers or just this one.
5. Now choose that preset in the dropdown list. The next time you will print something the preset will be automatically active, so it will print two-sided as default.