You can modify various output settings for existing Print Definitions that already exist in a Print Set. For example, if a Print Definition was created using 8.5” x 11” as the Paper Size and you now want your output to be 11” x 17”, double-click on the Paper Size value for that Print Definition in the Print Set and select the new value from the drop-down list provided.
If changing values like Paper Size or Scale, you might need to apply a Print Style that performs a Maximize so that your graphics properly fit the new size.