I guess that this is a very easy question, but since it is something I have never done before, I prefer to double check with the experts!

My wife and I will be visiting the UK for a few weeks in March and we will book a CX ticket HKG - LHR - EDI - LHR - HKG (the Heathrow - Edinburgh flights will of course be with BA). I will book the tickets in the usual way, with same day connections in both directions. However, if we decide to stop over for a few days in London on the way back, can we change the ticket so that there are a couple of days between the EDI - LHR and the LHR - HKG flights? It will be a modifiable ticket, but I am suddenly wondering if I can still split the return like this. Or if we do, will it completely mess up the pricing so that we would be hit with a massive extra amount to pay, over and above the usual price conditions?

Thanks for your advice !