removing wall

Another problem I'm having is this..... I need to replace a main feed 12/2 from the meter box, as its old wiring and the cable orginally ran up a dividing wall up into the attic were it supplies power to kitchen lite, but I have taken the dividing wall away to open the kitch/dining room up. I.m pretty certain this cable comes directly from teh meter box as it is marked kitchen lites, is it possible somewere under the kitchen floor ( meter box is in basement) it might be supplying power elsewere?.. and I assume IF I turn the main breaker off it is safe to remove the circuit breaker for the kitchen lites and replace the old cable with the new one? any advice would be appreciated, thanks

 

It is definitely possible that it supplies something else. Turn off the breaker and see what else is affected.