EPW files are essentially rearranged TMY files, and I don't see anything in the TMY-2 data elements or TMY-3 user guide that correlate to atmospheric composition of air vs. CO2 and resulting change in convection coefficient values. As such, I would recommend adding the SurfaceProperty:ConvectionCoefficients object to your IDF, which can allow users to set interior and exterior convection coefficients using multiple options:

• constant value
• time-based schedule of values
• custom curve of values (defined by SurfaceConvectionAlgorithm:Outside:UserCurve or SurfaceConvectionAlgorithm:Inside:UserCurve object)
• same overall models used by SurfaceConvectionAlgorithm:Outside and SurfaceConvectionAlgorithm:Inside objects (Simple, SimpleCombined, TARP, AdaptiveConvectionAlgorithm, etc.)

Note that this convection coefficients object can only be applied to a single surface.

The SurfaceProperty:OtherSideCoefficients object is another option, but it can only override exterior surface convective heat transfer coefficients and/or air temperatures.