You can spawn BO3 with the /tc spawn command. To export them again you would need to select and Export them again.
Again, with your Trees, you have the Offset defined. Just add a "Block(0,OFFSET,0,DIAMOND_BLOCK)" (If your Offset was -8 you would put 8 as y coord in the Block) at the start of each object, and run BO3 BulkEdit. Doesnt have to be in Order.
Edit: If you want, I can also do that for you. Its not much Effort.