My teacher's advice is reflective of what Malcolm says: dressing up is not being a ngapa, and samayas are samayas--many ways of understanding samayas, many systems exist. But, for beginners, mantra practice, and samayas, are somewhat "aspirational." Even those who've had Direct Introduction in Dzokchen systems don't have "power over mantra" --or so I understand. One needs to do the intensive retreats, truly maintain samayas, and produce some sort of sign or have a recognized qualification that a given practice has been "completed" or produced results. Then, one "holds mantra" and one's practice is effective. Then, one is truly a ngagpa. In fact, "using mantra on others" prior to such sorts of results may be a nice, aspirational thing to do, or it may be delusional, depending.
Most self-designated ngagpas, empowerments or not, are merely aspiring at best, or playing dress-up or gaming someone, including, often, themselves.

