May a propeller spinner be removed/replaced as owner/pilot maintenance? It is not specifically mentioned. However the owner/pilot is allowed to remove and replace the cowling, and is expected to inspect the spinner and bulkhead for cracks.
No. Item 19 of the preventive maintenance tasks list in Appendix A to Part 43 specifically prohibits removing the propeller. OTOH, as you noted, that item does explicitly approve removing the cowling.