Booting from an external hard disk I am about to upgrade my mid-2012 MackBook Pro with a 500 GB SSD, and use the current HDD as external storage by placing it in an appropriate case that would allow me to connect it through USB later.

Rather than backing up my whole system and data, I thought I would just do the SSD upgrade, and hookup the external hard disk later and copy over my files and projects as I need them (one of the reasons I am considering this is that I have lots of files that I may not need now, but that might be useful to keep for the future... sort of hoarding but that's just how it is...rather be careful than sorry).

my question, is there anything I should consider, before converting my current HD to external? Like file system config or something? Is it really this easy as I am picturing it or should I really think ahead of time and plan for failures to access my HD as external drive, for example, for not having read/write rights or privileges.

EDIT: In the current HDD, I only have one partition used both for OS and Data.
Here's what I used to do back in the day when hard drives were swappable in MacBooks (and PowerBooks before, I'm old.)


Put the SDD in an external exclosure and connect it to the Mac.
Clone the HDD to the SSD.


Use SuperDuper or Carbon Copy Cloner, both are great and have generous trial versions.
You now have a full backup AND a functional bootable drive.

Swap the HDD with the SSD. 


The HDD is in the external enclosure. You can use it as a backup, both SD and CCC let you update/sync your clone drive.
Your Mac is now on SSD. Everything works just like before only much faster.



That's it! Enjoy!