Currently you can't. Will be reviewing either improving substitutions so it can be conditioned with an IF substitution or adding additional layout parameters for titles for CB 2.1. Best I can suggest is condition the title using a substitution IF usage based off the user being logged in or not, but it's not going to be specific to registration. Example as follows for such a usage.
[cb:if user="#displayedOrMe" user_id<="0"]I am A GUEST.[/cb:if]
[cb:if user="#displayedOrMe" user_id>"0"]I am NOT A GUEST.[/cb:if]
See the substitutions tutorial below for more substitution usage information.
www.joomlapolis.com/documentation/279-community-builder/tutorials/18353-using-substitutions-throughout-cb