Can I upgrade my copy of GTAV to a Collector's Edition or Special Editon?

Usually Rockstar releases these bonuses as DLC later, but you might have a while to wait. For example the Red Dead Redemption pre-order bonuses became available as paid-DLC about a year after the game's release (Release May 2010, DLC April 2011).

Source: http://reddead.wikia.com/wiki/Pre-order_bonuses