It wouldn't be hard to change, as it has already been done so in the past. When I first got on STEEM, the payouts were originally done 24 hours after posting, and a second time 30 days after posting, but that has changed to 7 days now. It would require a hardfork though because of how big of a change it is and so 17 of the top 20 witnesses will need to agree to it.
So to simply answer your questions, its possible, but would require a large majority of the witnesses to accept the change.