Hi,
IAORA & TAORA are not used by SAP system outside of upgrade/reorg/system copy
It should not be a problem to update them afterward (778784 - Inconsistencies between data class and database container)
I do not think setting compression a tablespace level is a good option, I thinks it is better to only compress only the 20 biggest tables / index (index compression has to be performed explicitly it is not inherited from tablespace attributes => 1109743 - Use of Index Key Compression for Oracle Databases).
Check the remarks to that blog Get more benefited from ACO
Regards