Whenever you then put in place the portfolio all over again by borrowing $S_ t_1 $ at level $r$ you can realise a PnL at $t_2$ of Column nine: Effects of cancellation / Modification – PnL from trades cancelled or transformed on the current working day "hitparade.ch - Discographie PNL". https://www.youtube.com/watch?v=qMmsQ4kKgY4