If I drop and recreate a table with two additional fields, will the journalling be cleared out too?
Also will the jounalling be enabled when I recreate the table?
That depends on how journaling was set up previously. If this is a SQL schema, then it will probably be reenabled. Or if not a schema, then if the library was assigned a default journal, it will probably be reenabled. Otherwise, probably not.
...the journal extract procedure will crash if we extract journals containing entries for different layouts.
Can you describe the "journal extract procedure" a little? That may have a significant impact.
When you do the DROP, you will need to end the jouirnalling since there will no longer be an object to journal.
When you do the CREATE, you will need to start the journalling again..
The old journal receivers can stay on the system if you need them.
You will be starting a new receiver when to do the STRJRN.
I am not sure what journal extract procedures you are asking about.
It this answer did not give you what you need, please give us more information on the extract.