My thoughts in passing …….. – it would seem to me that, in principle, the owner can do it as long as he doesn't affect the common property.
There would be some technical items + details that the OC is probably within it's rights to get cleared up before the works go ahead, things like:
– what fixings has he made / does he intend making to attach his false ceiling and false wall to the common property roof slab and common property walls?
– has he ensured that the kitchen drainage goes to the sewer drain stack and NOT to a 'conveniently close-by' stormwater downpipe?
If you have concerns about noise being transmitted across the walls and floor to adjacent bedrooms, then the real issue is the (possibly poor acoustic resistance) quality of the original construction rather than what is happening sound-wise either side of the wall or slab. In short, why do you think that it makes a difference if his room is a kitchen and not the original bedroom? (and if he is moving his kitchen to a location that is 'surrounded' by existing bedrooms of other units, then conversely is he moving HIS bedroom to a location that will be 'surrounded' by the kitchens of those other units?)