Yes, you can fill a HPA tank with CO2, but once you've done it, it can no longer be used for HPA.
Due to the cold temperatures of liquid CO2, there is a chance the aluminum (yes, a carbon fiber wrapped tank has an aluminum inner shell, the carbon fibre is just there to give it strength while remaining lightweight.) inside the tank will shrink too much causing it to seperate from the carbon fibre. This greatly reduces the tank's strength so it can no longer be filled with HPA (Which is at a much higher pressure than CO2! 3000+ PSI compared to CO2's <1200 PSI).
So is it worth to fill up an expensive HPA tank with CO2 making it useless for anything else? I'd say no...