Bolt cutters would be the answer, but...
Perhaps you are on to something. Cut off the old locks and replace them and keep the keys. I wonder how long it would be before anyone, in authority, noticed and changed the locks?
There was a very bad fire here in Fortitude Valley in Brisbane a couple of days ago. Fortunately the buildings were only about five stories high. A young man and two young ladies were trapped on a balcony with seconds to spare. The bloke said that his only choice was to JUMP off the balcony into some bushes below as he knew that the fire would get him if he did not. I thought of you cruisemonkey when I saw him on TV; I thought that at least you would now be able to throw out your rope and climb down. Fortunately he had dialled emergency services earlier and they directed a "Cherry Picker" to the balcony. Would you believe that this piece of equipment BROKE just after rescuing these people and there was not another suitable one around if it had been needed.
I can tell you that a lot of questions are NOW being asked as they realize that they need MUCH more in the way of how high they can reach. They only just reached these people.
Does anyone on China make rope ladders which could be purchased by someone who would not be as agile as cruisemonkey?