Eigentlich recht einfach:
Delphi-Quellcode:
var
FS: TFileStream;
begin
..
FS := TFileStream.Create(DateiName, fmOpenWrite);
try
FS.Position := 28;
FS.Write($10, 1);
FS.Write($27, 1);
FS.Write($00, 1);
FS.Write($00, 1);
FS.Write($10, 1);
FS.Write($27, 1);
FS.Write($00, 1);
FS.Write($00, 1);
finally
FS.Free;
end;
...

...
P.S.: Ist aus dem Kopf, anstatt Write evtl. WriteBuffer oder so

P.P.S.:
Dec->Hex