If an addition is bestowed to a magic stone resonator, the addition will remain bestowed to the magic stone even after it loses the resonator typing. However, any effects that rely on a "bestowed resonator," as well as effects that rely on an "as long as this card is not bestowed" clause, will not apply. In addition, because the addition is still bestowed, it cannot be bestowed to another card.
Ex: If "Shackles of Ice" is bestowed to a magic stone resonator, the magic stone will not be able to rest for will. When the bestowed magic stone is no longer a resonator, "Shackles of Ice" will fail to do anything.
If a magic stone that has been turned into a resonator with "Grusbalesta's Secret Technique" would be:
...sent to hand or the top of the main deck, it goes to the top of its owner's magic stone deck instead.
...sent to the bottom of the main deck, it goes to the bottom of its owner's magic stone deck instead.
...removed from game or sent to the graveyard, it still is.