When we accept a PR with some bug items attached, VSTS will change the status of those bugs to "Done". This is not really good for our workflow, as we would the bugs' status to change to "Ready for QA", and only the QA engineer would set it to "Done".
How can I change workflow so that the status is not set to "Done" whenever a PR is accepted?
When you complete the pull request， there is an option to Check Complete linked work items after merging to complete any linked work items.
However, when you selected this, VSTS will only auto change the work item status to done.
We do not have the ability to be able to specify the work item state after it is completed to something, other than Done.
There has been a related uservoice, and you could vote up it, TFS PM will kindly review your suggestion:
Customize Work Item State after PR is closed
