Are they all the same length? If so you can do
transform(df, :Name => ByRow(split) => AsTable)
then rename them after
in DataFramesMeta this is
@rtransform df $AsTable = split(:Name)
EDIT: Even better
transform(df, :Name => ByRow(split) => [:first, :middle, :last])
or
@rtransform df $[:first, :middle, :last] = split(:Name)