Hello- I wish to convert my 220v circuits to 110v as I have brought
natural gas into the home leaving free dedicated circuits from the old
elec. dryer, range and water heater.

I intend to switch out the breaker to a single pole 20 amp attach the
black wire to the new breaker and the second hot (red) I will lable
white and attach to the rail. The new 110 outlet I would rewire
normally. Is this procedure up to NEC snuff?

What if I needed a longer line and spliced (inside a junction box) to a
smaller gage wire such at 12/2 romex?

Thanks.