In New York, town control over zoning and land use within its borders is governed by New York state laws. The state legislature delegated legislative and administrative control over land use to incorporated villages within towns, and to towns themselves for the areas in such towns that are outside incorporated villages. Villages and towns are legal entities which can sue and be sued and thus be held accountable legally for the consequences of their decisions. The theory is that legislative and administrative control over land use is an exercise of police power (to regulate public health, safety and welfare) and that such delegation of authority by the state is limited to duly elected legislative bodies.
Accordingly, while allowing a portion of a town's unincorporated area (e.g. Edgemont) to have exclusive legislative and administrative control over zoning and land use would be an option worth considering, it does not appear possible. Based on our research, it would require not just a local law (which a subsequent town board could repeal), but an amendment to state law authorizing all towns (or just the Town of Greenburgh) to even pass such a local law in the first place.
We have not found any example of that approach in any town in New York. For Greenburgh to even try to get such an amendment enacted, it would have to make a "home rule" request to the state legislature in Albany, and demonstrate to state officials that such a request to cede legal control over an unincorporated area of a town to unelected representatives of an unincorporated segment of that town only to make legally binding land use decisions, and to do so without giving other unincorporated area segments equal treatment, is even constitutionally permissible.
There are already ample laws on the books in New York giving residents of unincorporated areas of towns in New York the right to control zoning and land use by incorporating to form their own villages.