provider/aws: Allow DB Parameter group to change in RDS

builtin/providers/aws/resource_aws_db_instance.go

@@ -170,7 +170,6 @@ func resourceAwsDbInstance() *schema.Resource {
 				Type:     schema.TypeString,
 				Optional: true,
 				Computed: true,
-				ForceNew: true,
 			},
 
 			"address": &schema.Schema{
@@ -456,6 +455,12 @@ func resourceAwsDbInstanceUpdate(d *schema.ResourceData, meta interface{}) error
 		req.MultiAZ = aws.Boolean(d.Get("multi_az").(bool))
 	}
 
+	if d.HasChange("parameter_group_name") {
+		change = true
+		d.SetPartial("parameter_group_name")
+		req.DBParameterGroupName = aws.String(d.Get("parameter_group_name").(string))
+	}
+
 	if change {
 		log.Printf("[DEBUG] DB Instance Modification request: %#v", req)
 		_, err := conn.ModifyDBInstance(req)