Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

procedure ReplaceText(Edit: TCustomEdit; strOLD, strNEW: string);
 var
   x, Position: integer;
   tmpstr, tmpstr2: string;
 begin
   tmpstr := Edit.Text;
   for x := 0 to Length(Edit.Text) do
   begin
     if Copy(Edit.Text, x, Length(strold)) = strold then
     begin
       tmpstr   := Copy(Edit.Text, 0, x - 1) + strnew;
       Position := x;
     end;
   end;
   tmpstr2 := Edit.Text;
   if Position <> 0 then
     Edit.Text := tmpstr + Copy(tmpstr2, Position + Length(strOLD), Length(tmpstr2))
   else
     Edit.Text := tmpstr;
 end;

 // Example/Beispiel: 

procedure TForm1.Button1Click(Sender: TObject);
 begin
   ReplaceText(Edit1, 'OldWord', 'NewWord');
 end;


 // With the StringReplace function: 

procedure ReplaceText(Edit: TCustomEdit; strOLD, strNEW: string);
 begin
   Edit.Text := StringReplace(Edit1.Text, strOLD, strNEW, [rfReplaceAll]);
 end;