When the chicken pox has crusted over that means your not contagious anymore, but if you accidently scratch one off does it become contagious again?

Unlikely: The contagious period for cpx is considered the first week after eruptions start.By that point,the body has surrounded virus with antibodies and they go to the skin surface to die (in blisters)The early blisters do have contagious viral particles but most of what you would get pulling a scab off is just body serum, with no viral particles.It would be a reasonable precaution to wash/cover that area