Yes it's possible to change your Performance Policy association to a volume after it's created, and even when it's been written to. The only caveat is that you cannot change the Policy to another with a different block size association.
For example you could change a volume from "Default" to "Hyper-V CSV" as they both share the 4K block size association. However I believe in your example given SQL Log and Exchange Log are throwing an error as the former is 4K yet the latter is 16K.
Other settings such as Caching & Compression are not a restriction and changes on these settings will take effect on all new writes/reads that occur on the volume after being changed.
I hope this helps!
Hi John, may i ask the reason why you want to make the change? If you plan to mix workloads on the same VMFS volume - then the best practice is to stay with the lowest block size for the mixed workloads. It's always best to use small block size as common denominator as using the opposite would mean allocating large blocks for small read/writes (more overhead, less optimized)