Haven't seen the file or script but if you remove that line it should open in 12. What happens after the conversion, well, you'll find out. There may be scripts that will produce errors, etc.
Note that pre-12 and 12 do not open each other's files and that a file converted or created in 12 cannot be opened in 11, 10, 9, 8 or 7.
Create a Folder named Converted to 12 (or preferred name) and save the converted files into this folder so as to keep your other files intact and without change.
I've worked with those files. I think they'll convert and function fairly trouble free, but as Jack said, "you'll find out" when you convert and try them out.
I tried originally to simply change the version number from 11.99 to 12.99, but that did not seem to work. So, I simply removed all the code in the Open Script dealing with the Version Check. I did this, of course, using FileMaker11. (I first copied all the FTS traiing files from an FTS11 folder to a new FTS12 folder and worked on the copies in the FTS12 folder.) I then opened this file in FileMaker12 where it was recognized and then converted to the FileMaker 12 format. I did that for Module2 and worked thorugh the lessons in that module using FileMaker12 without encountering any difficulties. I just repeated that exercise for the example files in Module 3 and Modue 4 and so can now continue working through the FTS series using the new FileMaker12.