one more time but step by step. i laid this out earlier.
1. copy and append the file.
2. do nothing with the order except rename it.
3. explore order, go to the scans folder find the Preparation scan with the temps on it, copy it and move it someplace else and rename it so you dont get confused.
4. make a new order scan your case, but on the order sheet choose the box for adding additional scans, and pick the file you made in step3.
5. you will have to do an alignment of the scans because 3shape never sticks with one set of co ordinates. i hope your two scans have at least 3 teeth or tissue landmarks.