When you create a data archiving process for a semantically partitioned object, the process applies to the entire object.
Tab: Selection Profile
The partition criteria are listed under Additional Partitioning Characteristics and cannot be changed.
Time-Dependent Partitioning
With time-dependent partitioning, whole partitions can be archived, with the result that these partitions are empty. You can then either delete or repartition thsese partitions.
More information: Repartitioning Semantically Partitioned Objects
If you decide to repartition, you cannot reload the archived data because the relevant partitions no longer exist. You need to repartition again to recreate the old partitions.
Non-Time Dependent Partitioning
With non-time dependent partitioning (by sales organization, for example) only parts of the partitions are archived. This does not result in any empty partitions (as opposed to time-dependent archiving).