Yes, it is possible to expand or extend the subnet CIDR of an existing Azure Databricks workspace without creating a new one, but this capability is specifically applicable if the workspace is deployed with VNet injection.
For workspaces that use VNet injection, you can request an update to the CIDR range of the subnet associated with the workspace. To facilitate this change, it's essential to contact your Azure Databricks account team. They will assist you in making the necessary adjustments to expand the CIDR range (it is not self-service) and ensure that the additional IP addresses are available for your workspace's use.
However, if your Azure Databricks workspace is not integrated with a VNet, you will need to create a new workspace within a larger VNet that can accommodate your workload's requirements.
In summary, for VNet-injected workspaces, the CIDR range can be expanded via a request to the Azure Databricks support team, while non-VNet injected workspaces would require setup in a new VNet to increase address space.
Hope this helps. Cheers, Louis.