Much like you would do with some of your online passwords, it is sometimes advised to change your code now and again. When you do this, you will want to write down your new code to ensure that you do not forget it. But, regarding how many times you can do this, there is not going to be a limit.
This is one of the coolest aspects of these locks, quite frankly. There is no reason to change your code every day, but the fact that there is no limit is a nice touch.