1.VRB02KT: Is it varying more or less than 180°? 2.VRB03KT: Is it surely varying more than 180°?
Based on these criteria, is there a way to identify if a variable 2KT wind is varying less or more than 180° when the indication is just VRB02KT?

No, there is no way to tell. And you don't need to tell. The wind velocity is too small to have any operational impact.

If the wind intensity following a VRB indication is 3KT or more, can I assume it is varying more than 180°? Since this excessive variation in direction (not the relatively low intensity of 3KT) is the reason why the station can't measure the mean direction precisely.

Yes, that is safe to assume, as per the definition you quoted.
Remember the values you see in a METAR are average values over a period of time. If you need the immediate wind, ask the tower.