Hi Janne,
Use the following code snippets to copy the styles and formats of all cells in a row to another row.
[C#]
//Copying the range with styles.
sheet1.Range["A1"].EntireRow.CopyTo(sheet1.Range["C3"].EntireRow,ExcelCopyRangeOptions.CopyStyles);
Here is the sample for your reference:
Copying.zip
Please take a look at the sample above and let me know if you have any other questions.
Best Regards,
Melba