docs: def change_prior(self, **kwargs):
          """
          Changes existing priorfactors.
  
          If given keyword isn't already in priorfactors,
          then will be ignored.
          """
          for kw in kwargs:
              if kw in self.priorfactors:
                  self.priorfactors[kw] = kwargs[kw]
                  logging.info('{0} changed to {1} for {2} model'.format(kw,kwargs[kw],
                                                                         self.model))