When doing MK Ultra or Monarch programming, the personas and triggers are implanted by suggestion just like in hypnosis. However, unlike Hypnosis they are done at two much deeper trance states that you can't just talk people into.
I think this is where electronics comes in. The programmer monitors brain waves to detect when the subject is in one of these two trance states. So there are likely electronic ways of encouraging the brain to settle into the desired trance level by bombarding the brain with the right frequencies to encourage the brain to resonate at the trance frequency. Drugs can also help because they make the subject more relaxed and pliable.
Nevertheless, time is needed for programming. Once you have given the suggestions they need to be exercised which means bringing the subject out of trance, giving the triggers, walking through role playing, and then more trance to reinforce suggestions.