Wire nuts safe to cap off live circuit
Yes, it's safe and code compliant to cap the wires in the box with wire nuts.  Just fold them to the back of the box so they're out of the way.
Most people wouldn't worry about this in am million years, but wire nuts have a rating for the combinations of wires that you can use with the wire nut, and some wire nuts are rated for single wires.  The little gray ones like Ideal 71B are rated for a single #14 and the Ideal black 59B are rated for a single #12.  I find the little blue wire nuts hold a single #14 or #12 solid or stranded fine and keep them around just for that purpose, but they are not rated for that.  Call me a renegade.
Some people cap wires with wire nuts without stripping the wire, but they hold best if you strip the wire so the wire nut bits the metal not the insulation.