You could edit the keyboard mapping and make F9 Dead ([dead]).
So far that’s all I can think of.
If you do that, F9 will not work for any application.
Why do you want to do this?
We have questions about removing the command line, which is easy, but this is the first of this nature.
Although it’s not certain what you want, the most common method is to have the job set as LOG(2 *n *n). The “Level” of the job LOG() attribute can be set from 0 up to 4. Level 2 is the highest level that omits previous *REQUEST messages from being retained in the joblog. (Commands are implemented as ‘request’ messages.)
Set the level to 2 or lower to avoid having commands available for retrieval.
This can be done with a CHGJOB LOG(2 *n *n) command or by the related attribute of the job description. The CHGJOB command only affects the job named on the command. Setting the job description attribute will affect every job that uses that job description from that moment on.
Note that limiting what’s retained in the joblog will also limit analysis of possible problems.
The level can be set higher or lower while a job runs. You might set a low level at one point in order to avoid logging some items, then raise the level later in the same job to start logging again.