by definition a clear coat is going to be glossy or at the least a satin fininsh.
Just scuff it up with some 0000 gauge steel wool (found in woodworking hobby shops) this will dull the finish without affecting the integrity of the finish. i would just be sure to rinse it off well before putting it in with herps if the finish is not toxin free. also depending on what you are finishing, there are other protectve products out there that will seal without leaving a glossy finish. caranuba wax is a good example.