Changing the data class won't have any impact at DB level on an existing object, it won't change the tablespace used to store an existing table.
It will only have an impact for tables that are not created yet at database level.
When changing the data class of an existing object, if you are willing to change the tablespace used to store that object, you will need to use BR*Tools at OS level to move the table to an other tablspace (reorg).
Regards