2 yrs ago, cerebellar tonsillar Herniation after tumor resection: can this cause Chiari Malformation? A lot of recurring symptoms like pre-resection.

Imaging? Recent imaging would be very helpful to clarify some of the symptoms that you currently display. Low-lying tonsils after a suboccipital craniectomy for tumor resection may suggest cerebellar sag not necessarily Chiari malformation.
Chicken vs Egg. When did the cerebellar tonsils descend into the foramen magnum ? Was this prior to developing a mass effect from the tumor or cerebral edema ? If so then we would consider Chiari. Usually there are other features like "Beaking of the midbrain tectum", elongation of the 4th ventricle, abnormality of the tentoral incisura, and interdigitation of the midline dorsal cerebral cortex with Chiari Type I.