The easy part is the fact that you should always get a /48. As such you don't have to redesign your network when you go to another ISP. You 'just' have to replace the first 48 bits in all the configuration files and presto. And that is the problem, configuration files with hard-coded IP addresses are all over the place, as such you will have to update them all and first find them. Key to renumbering is thus having them in a known place, then you can just s/oldprefix/newprefix/ and done. But now there is another problem: remote locations. For instance, you have DNS glue, that means you have to notify the remote DNS admins to update these. Or firewall rules and ACL's at a remote company, you need to convince them to update it etc etc etc. Thus while it is a bit easier, as you simply always get that /48, you still need to do the same amount of work in getting it done. For most home networks though, it should not be too difficult to renumber as you will have a minimum amount of configuration files and hopefully kept track of where things are. That is why, as long as you stay with the same PoP, you have a good deal: you just move your tunnel endpoint and presto, all keeps on working.