Family name spellings were changed for many reasons. My relatives were Dunkards, and they were known to change the spelling to distance themselves. More often than not, it was a case of an illiterate clerk interpreting from someone who didn't speak English, so whatever got written down became their name. I have one ancestor that showed up in 3 different censuses across a decade, under 3 different variations of the same name.
My family is technically French, from the Alsace-Lorraine area, which I believe was traded off between the French and Germans over the centuries. We've traced our roots back to Langensoulzbach, in France.