Is it possible to impact / override how a resource is compared for changes vs how it will be deployed? An example would be a config store that uses a "sentinal" value to trigger when config has changed - I want to set the sentinal value as part of changes other values, but I don't want it detected as a change itself.

You would probably need to create your own (dynamic) provider to achieve this behaviour.

Can you specify the provider per resource, or would we need to do something top level? Also, would we also need to subclass the resource (c#) or is there a "property bag" for extensibility properties

You can specify the provider per resource, using the provider opt. I always do.

Thanks for your help. I'll have a dig!