update to
5. You can not change the priority anyhow other than reprocessing the item!
Not like this but again very complicated...
I had 4 items in a row with abandoned proirity.
I manually change priority for the 1st item - the change gets accepted - OK.
For the 2nd item I change priority to the same value as I did for the 1st item - the change does not take effect. You need to change the priority to a different value so the change is accepted!
So you can not change priority to the same value for two consecutive updates.