If you leave a space more than half a wall on one corner, you can move the wall out of the way long enough to do as you want and then put it back. It's like the hassle of moving a big building first to get at one behind it, then putting it back. Takes a bit longer, but can be done unless walls are overfilled. In that case you will have to delete one section of wall to get at them and either replace it or do some moving so gap is where it doesn't show.