Programmatically change the magnification settings for a single notebook or for a specific stylesheet.

In addition to changing the magnification directly from the notebook window, there are a few other ways to change this setting.

Within the Current Notebook...

Use CurrentValue to see the current magnification of the notebook in use:

Use SetOptions to change the magnification from 100% to 150%:

Within the Stylesheet...

Open a notebooks stylesheet

To change a style in the current notebook, choose Format Edit Stylesheet:

Choose a style to modify

In the stylesheet that opens, choose the style you want to modify:

Edit the local style definition

Select the cell and go to Format Option Inspector... ( ) to open the Option Inspector. Select Notebook Options Display Options Magnification to change the magnification of the notebook to 150%:

Notes

To restore Magnification back to its default values, use SetOptions with the value Inherited:
Global and kernel session magnification settings can be changed by replacing every instance of EvaluationNotebook with $FrontEnd and $FrontEndSession, respectively.