Merge pull request #247976 from davidsmatlak/ds-ghi-104813

Adds note about parameters to Policy doc

Author: prmerger-automator[bot]

articles/governance/policy/concepts/definition-structure.md

@@ -137,7 +137,7 @@ see [Tag support for Azure resources](../../../azure-resource-manager/management
 The following Resource Provider modes are fully supported:
 
 - `Microsoft.Kubernetes.Data` for managing Kubernetes clusters and components such as pods, containers, and ingresses. Supported for Azure Kubernetes Service clusters and [Azure Arc-enabled Kubernetes clusters](../../../aks/intro-kubernetes.md). Definitions
-  using this Resource Provider mode use effects _audit_, _deny_, and _disabled_. 
+  using this Resource Provider mode use effects _audit_, _deny_, and _disabled_.
 - `Microsoft.KeyVault.Data` for managing vaults and certificates in
   [Azure Key Vault](../../../key-vault/general/overview.md). For more information on these policy
   definitions, see
@@ -191,6 +191,9 @@ you can reuse that policy for different scenarios by using different values.
 > **defaultValue** property. This prevents existing assignments of the policy or initiative from
 > indirectly being made invalid.
 
+> [!NOTE]
+> Parameters can't be removed from a policy definition that's been assigned.
+
 ### Parameter properties
 
 A parameter has the following properties that are used in the policy definition: