How to change Mac installation .dmg packages to default to duplex printing
There is a way, but it's driver dependent. You can change it by opening the .ppd file from the .dmg. This builds on the answer below. How to create a Customized Pharos Uniprint Popup Package for macOS
Once that package has been built, you would change the .ppd file, as long as the option is there inside the driver, to accomodate duplex printing by default.
Here's an excerpt from http://www.cups.org/doc-1.1/sum.html#2_1
Printing On Both Sides of the Paper
The -o sides=two-sided-short-edge and -o sides=two-sided-long-edge options will enable duplexing on the printer, if the printer supports it. The -o sides=two-sided-short-edge option is suitable for landscape pages, while the -o sides=two-sided-long-edge option is suitable for portrait pages:
lp -o sides=two-sided-short-edge filename ENTER
lp -o sides=two-sided-long-edge filename ENTER
lpr -o sides=two-sided-long-edge filename ENTER
The default is to print single-sided:
lp -o sides=one-sided filename ENTER
lpr -o sides=one-sided filename ENTER