Redding out is the same, and in the case (Stake 1- Stake 2) is negative, and will be the loss for all outcomes.
Just stick it in a spreadsheet.
In your case, the original backer stake at 1.5 was £20 (don't do it considering the liability).At later odds of 2.5, New Stake= 1st stake x 1st odds/2nd odds = 20 x 1.5/2.5 = 12Profit = Stake 1 - Stake 2 = 20-12 = 8 (whatever outcome)Redding out is