What modifications are needed in datadictionary to change the block size of an area?
You can make the datadictionary changes directly to PROD structure. However if a history of changes is required, then copy the structure to TEST first, modify the blocksize in TEST with the 3002 transaction then copy to PROD and catalog the database.
The PROD structure can be modified directly using the 1000 ALTER transaction which also updates the CXX without having to close the database.
Sample DDUPDATE cards to make the block size change:
The new blocksize will not take effect until you INIT and re-LOAD the area.
In Datacom 15.1 there is a new Alter Area Block Size (BA24) feature which allows a change to the block size while the data stays available.
See DocOps section 1000 ALTER Transaction
and Performing a Block Size Alter 24x7 or Online Table Move