Can I add unfaced insulation on top of faced insulation which is on top of cellulose?
The facing shouldn't be there in the first place.  The facing/vapor barrier should always be on the inside. ("Warm side")

Having the facing on the outside creates a moisture pocket - moisture that gets between the ceiling below and the facing above becomes trapped, and encourages rot and mold growth.

Remove the facing and then you can pile on more insulation to your hearts content.  Lay it perpendicular to the existing layer.