In taking Social Security claims over many years, I do not recall many,
if any, immigrants who just decided one day to take on a completely
different surname and did so. Most of the people I dealt with came in the
early 1900s, however, not as adults yet. And they were in NYC, their
likely portal of entry to the U.S. Perhaps people were more likely to
change their names informally when they moved to new areas, where no one
knew them. Many people did, of course, change their surnames, often to
make them sound less Jewish, and lessen the chance of discrimination
against them. But such changes, at least 20 - 30 years after the time of
which you speak, were done legally. After all, these folks had children
registered in school with the original name, owned property in that name,
etc. So even before Social Security, there would have been complications
in just changing a surname without doing it through the courts, especially
if it were a compete change. People often legally changed their names as
part of the naturalization process. Our ancestors would, however,
simplify spellings and such without such formal proceedings. Given names
were changed much more readily. Often teachers could not pronounce their
student's name and told the student they would call him or her something
else. Those names frequently carried forward throughout that person's
life. At least that's what many people told me.

Lynne Shapiro
Western Mass.