Done:

aklapper@phab1001:~$ sudo /srv/phab/phabricator/bin/bulk make-silent --id 3262
Configured job "3262" to run silently.
aklapper@phab1001:~$ sudo /srv/phab/phabricator/bin/bulk make-silent --id 3263
Configured job "3263" to run silently.

However clicking on the links above and selecting "Continue" in the sidebar, it says "This job is waiting for confirmation before work begins." Hmm.

Ah but now clicking "Continue" shows me that the job has now been set to silent:

I've completed both of the above jobs now, thank you! As an aside, is there a reason this isn't an option from within the UI?

I've completed both of the above jobs now, thank you!

@TheresNoTime Yay! Does that mean we could resolve this ticket?

As an aside, is there a reason this isn't an option from within the UI?

I'm not sure. I guess upstream developers at that time did not see a common use case for it. :-/