Multi-cluster istio deployment considerations

I’m new to Istio, and after reading the docs I understood there are multiple ways to configure Istio over multiple clusters. While shared control plane is what we will want to eventually have, I’m thinking to start with multiple control planes as it seems simpler to start with. My question is - is it possible to move from a multiple control planes deployment to a shared control plane deployment? What is the process for doing so?
My second question - does a share control plane deployment support active-passive deployment? E.g. when the cluster running the control plane is compromised, have a secondary cluster taking over and running the control plane instead of the compromised cluster?