[RKDinOKC]

Think all of the mac backup software lets you do bootable backups of a bootable drive while it is running. The ones I use do.

If I want to upgrade an internal drive...
Go to Startup Drive settings, choose the backup drive.
Shut down the computer.
Swap in the new drive.
Restart the computer (starts on the bootable backup)
Make a bootable backup onto the new internal drive.
Go to Startup Drive settings, choose the new internal boot drive.
Reboot.
As long as the new internal drive has the same name as the old one I'm good.
If I renamed it, it have to update the drive names in the backup schedules.

Way back in the olden days before OSX, to make a drive bootable you had to use a file editor and flip a bit on an invisibile file. If you made all files visible the icon for the file was the killer Rabbit of Caerbannog from Monty Python and the Holy Grail.