https://www.youtube.com/watch?v=tdx4-fBR5Sg

Change their behavior or train them. All that happens is you suppress it with a shock. But then it can come out in other bad and even worse behaviors-even aggression. shock is negative and painful to a dog (doesn’t matter if it’s for a second, still hurts and stresses the dog) and since you used it with the missionaries, she now has a negative association with them. It only takes one shock or bad experience to ruin their association with something. You effectively trained your dog to hate missionaries/possibly anyone in a similar suit. Dog sees missionary-dog gets shocked-dog assumes missionary is the reason-hates missionary.
Try teaching your dog not to bark with positive reinforcement. It takes more work and a bit longer of a process but you will not be damaging your dogs mentality and giving it negative associations or suppressing behaviors instead of teaching it to choose the right behavior. And yes, dogs do have the ability to make behavior choices. One way is (starting halfway through) to get the dog to bark on cue, then to be quiet on cue. It doesn’t work as fast like the video shows because it takes a few times before the dog truly gets and learns it, but it won’t stress the dog, won’t cause them pain, and you can control better when they do or don’t bark.
https://www.youtube.com/watch?v=3jcZKjb6zic