Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
The easiest way would be to convert the Publication to a PDF. You would have the option to print to a different scale. There is a Save as PDF add-in from Microsoft here:
You might try opening an A4 publication, copy/paste the objects from your poster. Lots of adjusting involved. This would be the only way you could retain the editing option.
Mary Sauer