The description itself would not be stored in HRP1002 when you display the posn in SE16 for HRP1002. The HRP1002 record provides a link to another table (I am not sure which one; you'd be able to see the table name in the prog module for PO13 txn).
The same applies to PA infotypes - text info.
Further when you create text infotype, the default start date for the PD infotypes is current date, which can be changed when creating.
If you want to change the eff.date, after creation, then in modify mode change the start/end date.
However for CC's and may be other controlling objects, when you need to change the validity period: For example, go to create (KS01 for CC create), enter the object id, validity period for the CC you need to extend, then enter the reference CC & Controlling area same as the one for which you need the change. Press Master data, it copies the data from the ref. CC which is same as what you want to change for validity period. Then press save. The records are combined, when you go back to display.