I'm not sure what decorators chalk is and I doubt the building regs thought about it either. If it is just around them not on the switches etc. then I don't see a problem.
There's no reason why you can't do it, but I wouldn't because in the event you want to remove the socket, half the plaster is likely to come away as well. Why not turn the electricity off, loosen the sockets, put Polyfilla on the plaster to make it up to be flat, let it dry, sand lightly, then screw the switch back?