You have an image composed of several layers and you want to create a new layer that has the entire image merged, while still maintaining all the seperate layers .
- Create a new layer and make it active. Link all the layers together, by clicking to the left of the thumbnails, you will see the little chain, indicating that the layers are linked (#1).
- Now while holding down the Alt/Option key, click Merge Linked from the layers "fly-out" menu (#2).
- You now have a new layer with the info from all the layers combined into it without merging the the layers (#3).