Would that be classed as 'like for like'?
Im 99% sure it is.
Moving of sockets/switches is allowed (by home owner) as long as you arent modifying the length of the circuit so I dont believe it requires a CC.
Swapping a non-dimmable to dimmable switch is considered like for like - same as swapping for a smart switch is.
It depends on exactly how the electrician does the job, if no additional wiring is required then just an ESC (Low risk ESC only) , if any of the wiring is extended then this triggers the "General Risk" which means a COC and a ESC although this is usually combined on one form.