Hi
Just enabling the flex flash on your local policy doesn't cause any impact on any of your servers so it is safely to apply it even though this policy is used by your c and b series servers.
But if you want to use a new policy and you only want to add this change to your c-series server, you need to make sure that your service profiles are not bound to an updating template because you will need to unbind them before you can apply make any changes to the service profiles.
to answer your question:
"its possible to have more than one Local Disk configuration policy?"
it is possible to have multiple local disk policies created in UCSM, but you can't have multiple policies associated with a template.
Let me know if this helps.