Does lift coefficient for maximum range change for a glider experiencing headwind?
Your first statement is correct, look at the lift vs AOA chart.  You go faster by pitching down (reducing lift and drag) and speeding up above Vbg(lift recovered now more drag), which effectively changes your trim and lowers AOA.  Why?  Because best gliding "Vbg" is all about covering the most distance per unit altitude, NOT time in the air.

In the most extreme case:  headwind = gliding airspeed you can see that no forward progress is made unless you glide faster.  Forward progress per unit altitude is:

(airspeed - headwind)/altitude  

Your new Vbg now factors in ground gain vs increase in parasitic drag.  The result is (obviously) you can't glide as far into a headwind, but (more importantly) you can help making your landing zone in a headwind by increasing your airspeed above published Vbg.