The Galaxy S10+ is already receiving its first software update. Chances are that the other S10 models will soon receive a similar one as well. The changelog includes Camera stability improvement, a performance bump for Fingerprint Recognition, and, what most important, the update “added feature to set the application or function which runs when the Bixby key is pressed”.
Samsung was clear in its intentions to enable the ability to remap Bixby button functions on its flagships. Furthermore, you will be able to remap the button and instruct it to react with an “Instagram mode”, which will use the native camera app to snap a picture and add it to your Instagram story.
Since the update is going out to a limited amount of devices already on the market (review and media samples), chances are that by the time yours is shipping, the update will be available for you to apply.