Decrease HANA memory on the fly

We are able to increase the memory allocated to the index server on the fly with the following command (alter system alter configuration ('indexserver.ini','DATABASE') set ('memorymanager','allocationlimit') = '300000') with reconfigure  , just wanted to check if it was also possible to decrease memory allocation on the fly .

Also can 'with reconfigure' be used with global_allocation_limit

ALTER SYSTEM ALTER CONFIGURATION ('global.ini', 'HOST', 'hanahost') SET ('memorymanager', 'global_allocation_limit') = '980000'

Thank you

Jonu Joy