[AND_REY]

Подправил:

Код:

Var
 S: String;
 P: Boolean;
 i, j, k: Integer;
begin
 P:= True;
 For i:= 0 To Memo1.Lines.Count - 1 Do
  begin
   S:= Memo1.Lines.Strings[i];
   For j:= 1 To Length(S) - Length(Edit1.Text)+1 Do
    if Edit1.Text = Copy(S, j, Length(Edit1.Text)) Then
     begin
      For k:= 1 To Length(Edit1.Text) Do
       S[j+(k-1)]:= Edit2.Text[k];
      P:= False;
     end;
   Memo1.Lines.Strings[i]:= S;
  end;
 if P Then Memo1.Lines.Add(Edit1.Text);
end;