Proviron is very mild in the way of effecting cholesterol levels. If you cholesterol levels are currently fine, there would be no problems with adding proviron into your cycle at a dosage of 25-50mg/day.
Proviron is one of the few oral steroids that is not liver toxic. It's a very mild steroid all around.
You can read up on proviron more here ->
http://www.evolutionary.org/proviron-mesterolone
Cholesterol levels in the body actually have very little to do with daily cholesterol intake. Poor cholesterol levels is the result of inflammation in the body.
The best thing you can do to keep cholesterol levels healthy on cycle is to follow a cholesterol friendly diet - low in saturated fats and refined sugars, and high in omega 3 fatty acids -
and to regularly incorporate hard cardio that really gets your heart rate up into your training program.
A good overall cholesterol support supplement certainly won't hurt either. Check out N2guard from n2bm.com. N2guard contains 43 ingredients designed to detox the body and keep cholesterol levels optimal.
Keep an eye on your cholesterol levels. If it gets high go to your doctor and get him to write you a cholesterol medication.