Yes I have some experience about the ?back bow? when changing to lighter strings! This happens sometimes, not only with Alembics, but in general with basses that have Ebony fretboard! Rosewood is probably the safest wood to use for fretboards ?.. but, I love the sound of the Ebony and have Ebony fretboard on most of my basses!
I use mostly 45-130 for 5 string basses and the Alembics have been OK with this. I think they are mostly set up for this gauges? I remember I have tried lighter strings like 40-125 on my basses and did get ?back bow? the truss rods where all open so it was a bit painful?.a friend of mine suggested to take it to service where they ?heat? the neck and then bend it somehow?. Or something like that?.. but I decided to do otherwise! I did raise the bridge, loosened the truss rod (they already where loose) tuned up the bass 11/2 step with regular strings 45-130 , so it was quite tight, and then let it be for a week! After that my bass worked with also lighter strings and no damage was done!