In theory it should be, but depending on how the container is written... it might just overwrite it again... I'm not really familiar with that aspect of containers.
As for your other question... they are user@hostname
root@OMV-MSI = you're user root on @OMV-MSI (which I assume is your server's hostname)
Mine at the moment... ken@openmediavault .. so I'm logged in as user ken, and my hostname is openmediavault
I think containers are essentially the same... in the numbers are simply the hostname for the container. Now where it gets that number, I have no idea, because it seems fairly random.
Don't confuse this number w/ the "Contianer ID" (sometimes you'll see this in online instructions). To view a container ID
If you just want to see all of your containers and their ID's...
Hope that helps.