Historical Building

The building code is not always taken over LEED requirements. Typically that only happens when the local building code is more stringent, not less stringent. You must include the exterior lighting and you must comply with the exterior lighting provisions of 90.1 as this is a mandatory requirement. A portion of this exterior lighting may be excluded from the requirements as a historic building (see Section 9.4.5 exception (i). This will not exempt all exterior lighting just the portion used to highlight historic features. In all cases you must include all of the exterior lighting in your energy model. It does not matter if something is exempt it must be modeled.

Exempt by ASHRAE only means that it is exempt relative to code compliance. It does not mean it is exempt for LEED except as it impacts mandatory provisions. LEED requires that you model all the energy use within and associated with the project. Nothing is exempt from that. You get to apply this exemption related to the mandatory provision of exterior lighting. Without it you would be required to be under the ASHRAE exterior lighting allowance. With it you can go over the mandatory allowance. For EAp2 you can't claim savings related to most exemptions (I am sure there are exceptions). In this case you are required to model the exempted lighting identically if you are claiming this exemption. You then have to seek savings related to other exterior lighting measures.