I am sorry to hear that you have experienced some problems trying to update your project settings.
The reason why you didn't see any items after the changes is caused by the changed statuses in the filters. I suppose that you have also updated the status groups (filters are created based on those status groups) for Story, Bug and Task workflows (check attached screenshot). To see your existing items you should remove status filtering - for example on the backlog select story and bug types and all(or none) status groups; or in the status groups in the xml include both the old and the new statuses. Then you will need to update all items in old statuses and set them to new ones.
For any further questions, do not hesitate to contact us again. If you need help managing the transitions, please send us both the original and the updated project settings so we can check them for any inaccuracies.
the Telerik team