What is the impact of repeated cooling and reheating of maple syrup?
The Cornell Sugar Maple research program website has a couple of relevant points:

If you find mold inside a newly-bought, previously unopened bottle of syrup, it is probably spoiled because of improper packaging.


  What causes syrup to have a musty or moldy flavor or smell? 
  Syrup that is improperly packed will mold, sour, or ferment. Syrup must be packed
  at 180°F and at a minimum of 66 Brix to avoid spoilage.


(Brix is the measure of sugar in the syrup.)

In your particular case where you see mold and want to reheat it, it seems that yes, you can reheat the syrup but it may crystallize a little:


  If a consumer finds bacteria, mold, or yeast growth on syrup he or she
  has purchased, he or she should remove the visible growth and reheat
  the syrup to a minimum of 180°F (do not boil), skim any visible
  growth, filter, and repackage the syrup. If syrup still has an
  off-flavor, it should be discarded. Also, the sugar content may
  increase causing sugar crystals to form.