No, it's locked in place.
I did some more playing around this morning and figured it out.
For a 4k screen, Windows 10 uses a 250% scale factor as default. Publisher must use that number to size the dialog box without actually checking the screen size to see if it will fit. If I change to 225%, it fits just fine. If I change to 300%, the buttons are completely off the bottom of the screen.
I ended up using a custom scale factor, because 225% is a little small for my middle-aged eyes. But a drop from 250% to 240% was enough to make the box fit.
For anyone else that finds this.
Right click on your desktop, chose Display Settings.
Find Scale factor and make it one size smaller (250% to 225%, for example). If that's a little too small for you, click on Advanced Scaling Settings and you can change by 1% increments.