Is the size of the double arrow sign (W1-7) changing?
In short, no.
Some folks have recently heard the double arrow sign is going to be a different size. The National MUTCD, the NYS Supplement, and the National Standard Highway Signs and Markings books show the standard size is still 48” x 24”.
If you wanted to put up a larger sign due to visibility or other safety concerns, the size would be 60” x 30”, still a ratio of 2:1 in width to height.
Cornell Local Roads Program MUTCD page
(shows how to order both documents that make up the MUTCD in New York State)