One way or the other, if you now add support for storing the pre-amp value, you will still get that these modules play wrong, because they originally weren't saved with this setting.
If you have to alter your song anyway, just change it to Mixmode 3, and it will most likely solve the problem. If not, then change the global volume or VSTi/Sample volume and that certainly will fix the issue.
I used the same thing to fix my old songs. Its a matter of seconds to fix your song, hit save, and its fixed forever. Really, there shouldn't be a need to store the pre-amp value.