I am replacing receptacles and switches in a remodel. While replacing a 3 way switch I discovered one of the conductors has a slice about 2 inches long down the insulation. I can see copper. There is not enough cable to pull and re-terminate. Its probably been like this since the house was built 25 years ago but I can't leave it. Is it acceptable to repair this by cutting the conductor off where the insulation is good and wire nut a 4 inch length of 14awg to reconnect the switch? Forgive me I do not typically do residential jobs and not familiar with best approach here!