Is it possible to change the fontsize when printing a notebook in the working environment?

For those like me who were confused even after reading Alexey Popkov's answer, let me provide more detail:

Click Format -> Edit stylesheet

A window will open that says "Private stylesheet for your_notebook's_name"

Copy-paste the following code below where it says "local definitions for style all: all"

Cell[StyleData[All, "Working"], Magnification -> 0.8]

A dialog box will appear that says "the text you are pasting corresponds to a cell expression..." Click YES

The text it adds now reads "local definitions for all styles in style environment 'working'". Note that it doesn't say anything about magnification anymore. THIS IS NORMAL. Close the window and your changes have been saved. Print your PDF (in "working" printing environment) and it works.

Based on this answer. Add the following to the private style sheet:

Cell[StyleData[All, "Working"],
 Magnification -> 0.8
]

Adjust the Magnification setting according your needs.