As of Epplus 7.0 you can create CustomIconSets with EPPlus

To do so, try e.g.

```csharp
using (var pck = new ExcelPackage())
{
     var threeIcon = wks.ConditionalFormatting.AddThreeIconSet(new ExcelAddress("A1:A20"), eExcelconditionalFormatting3IconsSetType.Triangles);

     threeIcon.Icon1.CustomIcon = eExcelconditionalFormattingCustomIcon.RedFlag;
     threeIcon.Icon2.CustomIcon = eExcelconditionalFormattingCustomIcon.NoIcon;
     threeIcon.Icon3.CustomIcon = eExcelconditionalFormattingCustomIcon.GrayDownInclineArrow;
}
```

```vbnet
Using pck As New ExcelPackage()
    Dim threeIcon = wks.ConditionalFormatting.AddThreeIconSet(New ExcelAddress("A1:A20"), eExcelconditionalFormatting3IconsSetType.Triangles)

    threeIcon.Icon1.CustomIcon = eExcelconditionalFormattingCustomIcon.RedFlag
    threeIcon.Icon2.CustomIcon = eExcelconditionalFormattingCustomIcon.NoIcon
    threeIcon.Icon3.CustomIcon = eExcelconditionalFormattingCustomIcon.GrayDownInclineArrow
End Using
```

This is also available with FourIcon and FiveIcon sets. The `OfficeOpenXml.ConditionalFormatting.eExcelconditionalFormattingCustomIcon` enum includes an option for all icons available in Excel. Note that Icons in excel are counted from the bottom up when editing a rule. So Icon1 will be