Trying to point out that their isn't a proper process involved with these changes. Rushing into anything doesn't help, that's why I am delaying the conversion to the 172.26 range for Bellville till 2019 (For old sites).
No point in renumbering if you sit with the same/more mess. That is also excluding the fact that it is a time consuming task.
My 3 point step is a good place to start and my contribution to this thread.