LT,
I'm not sure that I'm understanding correctly but here's my take on what you've written...
Files are independent. So if you freeze the tracks for my_file1.sgu and then save it, the tracks will be frozen. Now if you save it as my_file2.sgu, and the tracks are frozen, you'll have two files with frozen tracks.... namely: my_file1.sgu and my_file2.sgu. At this point in time, because the files have different names, the two files have no relationship to one another.
Now, if you unfreeze the tracks for my_file2.sgu and re-save it, this second file will generate a different backing next time you open it because the tracks are no longer frozen. When re-opened, the file my_file1.sgu, on the other hand, will generate the tracks as they were frozen because that information was recorded with it.
Hope this answers your question.
Regards,
Noel