How does Mr. Hooper’s conduct on the day that "The Minister's Black Veil" takes place contrast with his normal behavior?

I am not entirely sure that this question isn't a trick question that looks to force the answer to be a rebuttal. When the story starts, there is something different about Father Hooper. He is wearing a black veil that covers his face. That is the only difference in Hooper. Readers are told several times that his behavior was identical to what it normally was. Notice how the third paragraph describes Mr. Hooper's walk toward the church.

. . . and beheld the semblance of Mr. Hooper, pacing slowly his meditative way towards the meeting-house.

Readers are told that Hooper was pacing "his" way. A person's gait is unique like a fingerprint. That's why "gait recognition" is gaining ground as legal identification.
Readers are also told that Mr. Hooper's sermon was delivered in the same way that his other sermons were delivered. He's not a fire and brimstone speaker, nor is he highly energetic from the pulpit.

The sermon which he now delivered was marked by the same characteristics of style and manner as the general series of his pulpit oratory.

The audience may have received his message differently, but it wasn't because Mr. Hooper was behaving any differently. It had everything to do with the fact that Mr. Hooper decided to wear one extra piece of clothing that happened to cover his face.
http://biometricnews.net/project/gait-recognition/