I looked for ExcelPackage documentation to see what type Names[] collection returns and found that documentatios will come soon, or at least that is what they said back in 2007.
I suggest you use EPPlus wich is a excel library (xlsx only) that have worked great to me.
official link
Now, to set a value for each cell in a named range:
ExcelWorksheet sheet = _openXmlPackage.Workbook.Worksheets["SheetName"];
using (ExcelNamedRange namedRange = sheet.Names["RangeName"])
{
for (int rowIndex = Start.Row; rowIndex <= namedRange.End.Row; rowIndex++)
{
for (int columnIndex = namedRange.Start.Column; columnIndex <= namedRange.End.Column; columnIndex++)
{
sheet.Cells[rowIndex, columnIndex].Value = "no more hair pulling";
}
}
}