At present you can if your listings are on the old postage system and any new ones allow you to use custom postage
if they’re changed to simple delivery which could be any time ,then no you have to use the label provided
But if you have a phone that can receive qr codes from eBay you can get the labels printed for you and stuck on the package at the post office , for normal postage as it’s been till now or for simple delivery the new system
