You do know that you can add all the files to your .mix at one time, right.
I go to Xilog, then New > .mix file.
Then, under the tools menu, I think it's "List of Files" or something like that.
Select the last file, then Shift-Select the first, and all the files are added at once.
This only takes about 10-15 seconds.
I then use Find and Replace to change the BZ value.