Hi,
The access policy feature from Spark Management is unique and is by design co-managed with the local appliance. This means that the even if the policy is managed by Spark Management, it is not locked for editing on the local web UI. To ensure some admins will not be able to create rules, should be achieved with using specified roles. Consider looking into the self-serve portal feature that provides a web UI with only a small set of capabilities.
Regarding the migration of access rules from Smart-1, it is not possible at this time, moreover the access policy capabilities in Spark Management is more simplified comparing to Smart-1, which makes a migration impossible.
You can add external CA certificates to Spark Management to be distributed to the connected gateways under Settings -> Certificates. When a device is managed by Spark Management, the VPN certificate is automatically issued and maintained by Spark Management as long as the device remains connected to the service. This means that when configuring a VPN community where the center is managed by Smart-1, and the Spark gateways are managed by Spark Management, you will need to share the CA with each side. Where the center is usually configured as LSV.
I am also sharing an SK for how to setup a VPN community in Spark Management with an externally managed Check Point gateway: https://support.checkpoint.com/results/sk/sk177545