Sql-server – How to set the deadlock priority for a maintenance task created trough the graphical interface

This doesn't address your primary question but I can't help but propose a different approach than the one you're currently taking. You should be backing up the transaction log frequently enough that, in the event of a disaster, you won't lose any more data than your SLA allows. If you can afford to lose up to 30 minutes of data, then you should probably be backing up the transaction log every 15 minutes. You can certainly do this through the maintenance plan wizard (including picking which databases to run on, and one option is definitely "All user databases"):

Your current approach of switching to simple, running a shrinkfile, then switching back to full, is quite self-defeating. You're in full recovery model but you're not getting any of the benefits from it. Backing up the log throughout the day will keep your t-log size down as backing up the log allows space within the file to be re-used. If you don't need point-in-time recovery, then switch to simple recovery. This allows the space within the log file to be re-used automatically. In either case you shouldn't have to manually shrink the file anymore - which is very expensive process to repeat every night (never mind one that impacts users every time it auto-grows during the day).

You need to change the appropriate upstream precedence constraint(s) in the flow to On Completion instead of On Success.

This is done one of two ways:

1. Right-clicking the constraint on the design surface (shown below) and selecting the appropriate type from the popup menu.
2. In the Precedence Constraint Editor dialog (which you had open), select the appropriate type from the Value dropdown list.

In earlier versions than 2012, the constraint arrow will turn blue; in 2012, the arrow gets a more explicit "Completion" caption.

Now having said that, if you want to keep all of this in one flow, I would actually recommend using SQL Server Data Tools to create the package, because what you really need is a Sequence Container to put all the maintenance stuff in (keeping the existing On Success constraint types), and then connect the container to the backups task with an On Completion precedence constraint.

Alternatively -- and this is what I would usually do -- separate the backup portion of the process into a different subplan, and schedule it after the maintenance portion is expected to complete.