A few updates on this one, with USD in Toolbag 4.06 this is now easier. 1. You can export a copy of your scene as USD and import it into another scene 2. USD supports all of the light types in Toolbag, including the Sky 3. If you export USD, the sky HDRI image will be saved out - useful if you need to extract the sky to…
To op's situation, i open up m3 and m4 and redo the scene copying the numbers and settings when i run into this issue, yea an export situation would be less time consuming but this is the solution for me and possibly others if no one thought about it, there it is. (export what you can, though)