Kessner Family Genealogy Forum
That kind of minor spelling change is certainly to be expected, and I would consider KESNER and KESSNER to be equivalent. German names tend to get terribly fractured by English-speaking clerks. They are simply trying to spell phonetically the name a German speaker is telling them, so think of the *sound* and how it could be (mis-)interpreted.
I have found over 100 spelling variations of of my mother's German name, STRAUB! You can check them out at:
I don't think KESSNER/KESNER lends itself to so many mis-interpretations as STRAUB, but then, people are surprisingly creative. And remember that many mistakes are not those of the clerk in hearing and writing down the name, but of the reader transcribing the record. Many of these old records are very difficult to read.