The gemara says that you can't move a kli to put on to a muktze kli on Shabbos because batel kli m'hechano. The gemara also says if the muktze item has the potential not to be muktze later on Shabbos. Any time something becomes a basis l'davar ha'asur on Shabbos, you could put a davar
hamutar on top and then you could move the item. Therefore you can never be totally mevatel any kli m'hechano because you could always move it if you put a davar heter on top.
Correct! As you correctly observed, there are many cases where the Kli can be moved by adding a non-Muktzah object to it (MB 310:37) or by shaking off the Isur. However, since until the situation is changed the Muktzah is still resting on it, the Kli is Batel me'Hechano.
Also see MB 265:5, who writes that placing a Kli under a lamp to catch the oil is Mevatel Kli me'Hechano because one will not spill out the oil, and presumably one would not put any permissible item of importance on it either. If the Kli was placed to catch a falling wax candle there is no problem, as it will be extinguished as it falls and you can shake it off immediately. However, bits of burning wick falling would be Mevatel the Kli as they cannot be shaken off until they go out.
We see, then, from the Mishnah Berurah that the Isur of Mevatel Kli me'Hechano applies if there will be some stage that it is forbidden to move the Kli even if afterwards it will be permitted.
This reasoning appears in Tosfos, 43a, DH Tevel, who writes that even though if the egg was removed the Kli would be movable, but since the Kli is holding the Muktzah right not, it may not be moved.
Kol Tuv
Ilan Segal