Can I develop pyelonephritis & chronic UTI from postpolypectomy/peritonitis post-colonoscopy?

Complicated. If the intra-abdominal infection involved the kidney in some fashion then pyelonephritis could conceivably occur, but this should be treatable. With this process the presence of a foley catheter during your management can predispose to uti, as can bacteremias which occur during the infectious process. None of these would necessarily create chronic uti, but anything is possible.