Special care needs to be taken when you edit job definitions that have already been submitted and have not yet started or job definitions that have been submitted with a submit frame. This is especially true when you edit the parameter list by adding non-Nullable parameters or by changing a Nullable parameter to non-Nullable. If a job is resubmitted by a submit frame and the parameters are not valid, for example when a non-Nullable parameter contains a null value, the job will be aborted and reach the Modified status, which will require human intervention.

Every time a job definition is submitted, a slave copy of the job definition in its current state is made and attached to the job. The user cannot interact with this slave copy. When you edit the master job definition before the job has reached the Dispatched status, the new job definition will be used. However, when a job definition is used several times in a submitted job chain, the new job definition will only be used when the first occurrence of the job chain job has not reached Dispatched at modification time. This has been implemented to allow job chains to remain consistent.