Basically yes. If you have laid at an exchange that has a cash-out option then you can just cash out. If at Matchbook then you need to place a back bet and there are calculators/spreadsheets on OM and PA that allow you to calculate that.@jkg-jkg so basically you couldcash the lay bet out when the team you have backed go 2up?
Those calculators also allow you to do partial cash out so you can lock-in some profit and then hope that the other side comes back and make a bigger profit. So last night I did a partial immediately and locked-in £100. When Arsenal scored the odds moved and I locked-in another £50. If Arsenal had drawn or won I would have been up an additional £150, but as it was I was down £60 on what I would have got if I had cashed out 100% at the beginning (a gamble but Arsenal coming back was a good possibility).
Of course these don't happen very frequently. If you back the favourite and they go 2UP you are likely to make £10 max, but if you back the other team you get a fair bit more as their odds keep up a bit even though they have scored twice (and the favourite coming back is a lot more likely)