Vitamin C has nothing to do with you being cold. That is just an unfounded >rationalization/bad guess<. Being cold when fasting is just a fact of any form of fasting because they all slow down the metablolism.
I wouldn't say you're starting on day 1 again from doing some orange juice. You kinda just eased your way to get digestion started again so just continue on the MC. I might just make a little hungry for a coupla days but thats just about all.
I have done more than a dozen 40 dayers but then again I haven't been dealing with major health issues. The supervision thing is a thing of caution cause many that fast might can be uninformed and either be fasting when it's contraindicated for their specific condition or they can "rationalize/second guess" all kindsa things when going through a healing crisis and make matters worse instead of understanding what is going on and either making a slight adjustment or just plain sucking it up and allowing the fasting process work it's mojo and eliminating the toxins that were causing the healing crisis to begin with.