Renaming partitions doesn't affect index status, global or otherwise. They stay valid if they were valid before the rename.
You don't need a primary key for interval partitioning. The constraints are the same as for range partitioning, with some restrictions. See Interval Partitioning in the concepts guide:
- You can only specify one partitioning key column, and it must be of NUMBER or DATE type.
- Interval partitioning is not supported for index-organized tables.
- You cannot create a domain index on an interval-partitioned table.
Note that the names for the partitions created automatically on an interval-partitioned table are system-generated. You can rename them after they've been created, but you cannot, in 11gR2, have them created with a name of your choice.