Is there a fast way to change ALL the gates thru the GSX interface to "both" as there are lots at YSSY or does it have to be done 1 by 1?
Of course there is. Just select more parkings on the left side of the tree-like list. If you select a terminal node, it will select all parkings in it, and if you select the ICAO code at the "root" node, it will select all parkings at the same time.
Then, every setting you change when multiple parkings are selected, will be applied to all of them. So, be careful to change ONLY what you really need to changed (the Pushback preference in this case), when multiple parkings are selected, then deselect them.