Of course you can.  If you wish to be removed from the Roster, just ask Crux, it’s that simple.

You will also be removed from the Roster if you are not reported as active by your local Group herald for two years, if you unsubscribe from Blazons, or if found to have engaged in serious misconduct.

Un-rostered people may act as stand-in tourney heralds, but their acting as Court Heralds or offering consultation advice is discouraged in the strongest possible terms.