This function adds a new XF record to the global format list and returns its id. 

If the format already exists, it won't be added again and the function will return the id of the existing XF. 

For example if you have:

Fmt:=FlexCelImport1.FormatList[15];
Fmt.Font.Name:='Courier';

and FlexCelImport1.AddFormat(Fmt) returns 33, then calling FlexCelImport1.AddFormat(Fmt) again will return 33 again, and no new format will be added. 

But while this code is valid:

FlexCelImport.CellFormat[1,1]:=FlexCelImport1.AddFormat(Fmt);
FlexCelImport.CellFormat[2,1]:=FlexCelImport1.AddFormat(Fmt);
FlexCelImport.CellFormat[3,1]:=FlexCelImport1.AddFormat(Fmt);
FlexCelImport.CellFormat[4,1]:=FlexCelImport1.AddFormat(Fmt);

It is more efficient to write

XF:= FlexCelImport1.AddFormat(Fmt);
FlexCelImport.CellFormat[1,1]:=XF;
FlexCelImport.CellFormat[2,1]:=XF:
FlexCelImport.CellFormat[3,1]:=XF;
FlexCelImport.CellFormat[4,1]:=XF;

To create a new format from scratch, you can use GetDefaultFormat 

TFlexCelImport Methods