Even if it absorbs and re-emits everything, that would probably be fine. Black body radiation is emitted in practically every direction, and only a miniscule portion of that would hit the Earth.

The bigger problem with absorption is potentially heating the material to the point of vaporization.

All that said, the most practical form of this would probably be something like a fresnel lense that uses refraction or a structure that uses diffraction to redirect the light rather than reflect or absorb it.