If you gauge the dosage correctly, the propaganda might nudge your opinion just enough to make you actually adopt the new action that you felt would adequately reflect your new beliefs, but not enough to drive you over the cliff into madness.

This sounds difficult enough to do reliably that I have to question whether it's actually a good tactic.

One thing I think may be helpful, that I've noticed some people here seem to practice; if someone says something to you which makes you think about revising your opinion, tell them so. You'll have forced yourself to take greater notice of your uncertainty, and have a social pressure to have something to show for your consideration after thinking about the matter further.