Hi,
Been trying to figure this out and tried reading the various different posts and guides but can't seem to get this working so sending up a flare 
My use case is -
I have a number of affected services linked to a parent, I'm trying to set up a rule whereby if someone adds a child it then recognizes this and adds the parent to the list.
At the moment I can only get it to either completely replace all the values and just add the parent I can't seem to get it to add the parent in addition.
Logic is, that for an incident, as a developer / logging tool I might say that API-X is impacted so add it to affected services.
As an incident / change manager I want to easily be able to see all tickets impacting that and also the system in general.
Rule runs like this -
- Affected Service added, call it Y
- Branch rule with a condition - object HAVING inboundReferences("Name" = X)
- Update Affected Services with the X
End result is Affected Services, Y, X are added to ticket.
Hopefully that all makes sense 
Thanks!