If you have a complete installation file, you do not need internet - disconnect before installing.
The updates do NOT run automatically, which is clear from the message box on a new update. Updates are downloaded and installed ONLY with the FSDT Live Update application. If you do not start it extra - except for a web reinstallation - NO automatic update will happen.
As a backup, they put the new "old" installation into operation and test whether everything is working.
If so, copy the entire AddonManager folder (6.07 GB) and name it, e.g. on AddonManager_BACKUP_Date.
This gives them a "reinsurance".
I did the same thing. Thus I have always 2 (!) Folder, which contain the complete GSX. If something does not work after an update, I rename the "new" AddonManager folder (which contains the new update) e.g. on AddonManager_MISMATCH, for example.
Then I change the folder name "AddonManager_BACKUP_Datum" back to AddonManager and, voila, GSX is running again WITHOUT the new (maybe buggy) update.