You can hack the DS_JOBOBJECTS table. Of course you would need to know the structure of this table, which is not documented. Further, since the parameters collection location within the record is not in the file dictionary for DS_JOBOBJECTS an SQL-based approach is not available; it would have to be programmatic.
You can export the job(s) with default properties, add the new parameters, the import the job(s) overwriting their existing counterparts.
Each approach has its own special dangers.
IBM Software Services Group
Any contribution to this forum is my own opinion and does not necessarily reflect any position that IBM may hold.
It can do a lot more than that. It can change all parameter defaults in a project from DEV values to TEST values in one click after a little setup. That way someone does not update the wrong database by accident.
I haven't spent a lot of time documenting all the features. Too much work. I would rather add value than sell more copies. You want it then buy it. It works well for me.