ASHRAE 90.1 does not allow savings to be claimed for measures which lack permanence. The calculation of luminaire wattage (Section 9.1.4) indicates that the wattage of fixtures shall be the maximum labeled wattage of the luminaire. However, if the lighting plans call for a particular fixture with a particular lamp then that is what should be modeled, according to Appendix G.
10/1/13 for rating system applicability.