It is possible, if you don't mind it cracking and falling off quite soon and giving you five times as much work as if you'd done it properly in the first place.
It is possible - You should coat the ceiling/walls with a thin downed coat of PVC sealer first then apply the filler, when it is dry give it another coat of PVA.
That said, if you could get the woodchip off it would be better.
Plaster over? Crazy. In places the woodchip might be barely stuck to the wall...the plaster will inevitably come off in the end. It isn't that hard to get off.
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