I'm not clear from your post as to which version you're on. In November 2011 NGS had been around for 6 months; and Picard 0.15 four months. There are no changes between 0.15 and 0.16 that would break your naming syntax.
http://blog.musicbrainz.org/?cat=9 has all the changelists.
If you are actually on 0.14 or earlier the main thing that would "break" your syntax would be the support for multi-disc releases. Without installing the "classic disc number" plugin; you could end up with multiple track 1s or track 2s on a release/album. Assuming you want the tracks for each disc in the same folder you'd want to adjust your syntax for %discnumber%. You could look at the default string for an example.
In terms of other fields; you could review the diff at http://wiki.musicbrainz.org/?title=Musi … ldid=38779 to see any other more fine-grained changes over the past year or so.
In any case, if you are that fearful, you can always back up your strings and scripts (good practice if they are complicated, in case your PC dies) and downgrade if you have problems.