The Australian AIP has the following guidance,
6.8 Block Level Clearances
6.8.1 Subject to traffic, ATC may issue block level clearances to facilitate operations in adverse weather or to allow flight crews to optimise fuel burn for an aircraft.
6.8.2 A block level clearance is cancelled or amended by the issuing of a new vertical clearance.
6.8.3 To request a cancellation of a block clearance when it is no longer required, flight crews should downlink a CPDLC request for the preferred level in order to enable ATC to issue the new vertical clearance.