Convert to Interval Partition from Range partition in 11g

Hi,

We have some tables with range partition in Oracle version 11.2.0.3.0.

We want to convert them to Interval partition so as to avoid yearly manual partition creation.

The current structure of range partition:

PARTITION BY RANGE (AS_OF_DATE)
( 
  PARTITION P201109 VALUES LESS THAN (TO_DATE(' 2011-10-01 00:00:00', 'SYYYY-MM-DD HH24:MI:SS', 'NLS_CALENDAR=GREGORIAN'))
..
..
)

Can we safely issue below statement:

alter table owner.table_name  set INTERVAL(NUMTOYMINTERVAL(1, 'MONTH'));

and convert the table to Interval partition? What is the 'NLS_CALENDAR=GREGORIAN' option in Range partition clause? Is it safe to modify it to Interval partition directly?