Can I place a filter like a Solar Continuum or other type, or reducer, flattener, or Barlow lens in front of a Solar Wedge?

NO you cannot because the concentrated light close to the wedge may cause the glass in these accessories to crack, paint to burn, or metal to melt.

 

ALWAYS put accessories like filters, reducing lenses, flatteners, bino-viewers, or Barlow lenses BEHIND the solar wedge, which is safest, and gives better performance.