Is there a way of saving the original app package used by Soft. to install an application (a blog, etc.), and then install it manually using Softaculous?
Or does a backup to the directory and database is suficient?
Another question, if I may: can we disable future updates of an application installed by Soft.?
If your purpose is to restore the installation from a backup in future the backup and restore functionality should be enough. The backup process backups up your installation as well as the database.
Regarding disabling the updates, by default the auto update is disabled and only if you enable the auto upgrade then Softaculous will upgrade the installation.