The gsu files are not on the snaps partition reserved for the OS. It the file you have to use for upgrade, os repair and diaster recovery process. So if something goes down you will be in trouble.
All debug cmds can be found by typing help from the debug screen (
http://ipaddress/admin/debug.cgi). I did not see any cmds related to the dns.
I do not know of any dns cmds but have not needed them either. I would think it's a problem with the DNS server and not the snap, if the info is not being updated. Then again it may have been a bug that was fixed in the later releases. Under my network port I can add Optional info for these, but have no need to since every thing is supplied through the router to all users. Now if you doing some kind of remap/modified host file I haven't a clue. If you know what file that needs changing you may need to change in on all drives using putty. But you will have to stop the process working inorder to do this.
Sorry I can't help you any more, but still learing as I go. What file did you modify to add a welcome screen to ftp users? and which dir is it located in.