I think you are talking about an upgrade install. Those have a long history of breaking things. You would have to be crazy to attempt one of those on a critical

I think you are talking about an upgrade install. Those have a long history of breaking things. You would have to be crazy to attempt one of those on a critical production system. What you would do for anything important is build a new separate system and then migrate to that once it is working. You can then migrate back if you discover issues too.