Can we set workflow notifications to in-app only for certain user populations?

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We are aware of the settings in BPM for controlling whether workflow notifications go to email or in-app, but we have some user populations that we do not want to receive emails because Oracle is not their primary HR system yet.  Is it possible to upload a preference to certain users to disable email notifications?

We know it would be possible to modify our approval rules with extra logic to not send notifications at all but we have a lot of rules and this is a temporary measure for a few months, so we would like to avoid that.