It looks like NO is the only component in the flue gas property package not presently supported in the natural gas property package. The Chapman-Enskog calculations for dynamic viscosity and Eucken correlation for thermal conductivity have been implemented in the modular property framework now. I'm not sure the heat capacity and Lennard Jones parameters all match, but I doubt they would produce significantly different results (so long as we're not using them outside their range of validity).

The only annoying thing is that the flue gas property package has mixture viscosity as visc_d instead of visc_d_phase and mixture thermal conductivity as therm_cond instead of therm_cond_phase. That means going through old unit models with find and replace to bring them up to standard.