So, you want to dynamically re-route tickets?

When Status changes and has value "Approved"
It has to re-route based on the category so it will gets attention it needs

I have a memory reading something about this by setting AUTO to something...
Manualy that works perfect. Gets re-routed like I want it to
But how to automate the manual proces:
- Incident in edit-mode
- pull-down "assigned"
- select --[auto]--
- save

Guido

If you have a table (or will be creating one)  that has a lookup for which queue/worker to route the ticket to depending on which category is selected, you can use the advanced assignment option of set properties to create a query which dynamically pulls the queue/worker. 

You need to use a Routing Rule instead of an Incident Rule.
In Routing Rules there is the checkbox "Only if not assigned" (or other way around like "Is assigned", don't have a system infront of me to check this right now.)
--> Use this one and your rule should be working, if you select "Auto" in the edit screen.

 Although , now that I am thinking about it, you should be able to set the assigned_to_worker_id = [auto] when the status changes and is equal to approved and it will route the ticket based on your routing rules.

 Well for one, you have spelled assigned wrong

Set "workitem_assiged_to_worker_id" to "[auto]"

Second, try using "Assigned worker", not "workitem_assigned_to_worker_id"

EDIT:

Actually if you correct the spelling mistake it should say Assigned Worker when viewing the rule.