In 12.2 a partition or sub-partition can be marked as READ ONLY at the time of creation (CREATE TABLE) or later (ALTER TABLE).
It must specify key word READ ONLY. READ WRITE is the default.
Example 1: (yxy is partitioned table)
SQL>ALTER TABLE yxy READ ONLY;
All current and future created partitions will be read only.
SQL>ALTER TABLE yxy MODIFY PARTITION yxy_p4 READ ONLY;
All partitions except yxy_p4 are read only.