Hi Peter,
It's technically possible to do that, yes.
You would have to isolate the VMOT pins from the 12V rail, and connect them to the higher voltage. Which traces to cut would depend on which AstroEQ version you have as the PCBs vary version to version.
Furthermore, the 100uF caps on the VMOT pins would have to be uprated. They are currently spec'ed for 25V which gives a nice overhead when operating at up to 15V. For running at 20V, I would swap them out for 35V rated capacitors.
The 0.1uF ceramic caps are already rated for 50V, so those wouldn't need changing.