[Closed] maxscript as modifier?

You can only wrap existing modifiers. With your example you could use an “Edit Poly” modifier and attach the resulting mesh into it. You can replace the modifiers interface with your own controls. But it wont be as nice and interactive as a real modifier.
More like how the different optimize modifiers in max (Pro Optimizer, Multires…) operate, with a “process” button to recalculate, in case of changes to the underlying mesh.