The only mods i kinow of is to attach a metal plate on the backside with epoxy and wrap over it and the back of the housing wit some mat. You are basically just fortifying the housing to make it stiffer and eliminate resonance, so you can go a little lower as far as xover point without audible resonance. So it des work to lower the Fs some.
Steve Head(Team Audionutz) used this approach in his competition vehicles and lent out the advice.
I did the same with my Usher midranges, just using mat. I was able to go from 700hz 12db slope to about 390-410hz 12db pushing some pretty hard volume without them popping.