no, not in that case we have here. this simply mixes an additional texture to the resulting skin.
however if one dynamically changes this shadowmap by writing into it it's possible to achive various interesting things

Pity it can't influence other objects. Maybe this will happen in A7?

Can the shadow map texture lower resolution than the main texture? If not, would it be much different from baked-on shadows in terms of texture memory consumption?

Much obliged,

it can be of any resolution allowed by the target gpu. in generally the technique used here has higher memory consumption as it is an additional texture. prebaked texture didnt work here, because the base texture is masked by a channel. if i'd do such shader from scratch i'd use a base texture unmasked (eventually with prebaked shadow) and then additional masked detail textures.

So.. if I had several objects using the same texture, from an external file (imagine one rock is repeated several times), in the long run I would indeed save memory if the shadow maps were 256x256 over the base texture, rather than several individually baked 1024x1024 textures.. is that correct?

yes