code: @Override
      public CacheSubnetGroup modifyCacheSubnetGroup(ModifyCacheSubnetGroupRequest request) {
          request = beforeClientExecution(request);
          return executeModifyCacheSubnetGroup(request);
      }
docs: <p>
  Modifies an existing cache subnet group.
  </p>
  
  @param modifyCacheSubnetGroupRequest
  Represents the input of a <code>ModifyCacheSubnetGroup</code> operation.
  @return Result of the ModifyCacheSubnetGroup operation returned by the service.
  @throws CacheSubnetGroupNotFoundException
  The requested cache subnet group name does not refer to an existing cache subnet group.
  @throws CacheSubnetQuotaExceededException
  The request cannot be processed because it would exceed the allowed number of subnets in a cache subnet
  group.
  @throws SubnetInUseException
  The requested subnet is being used by another cache subnet group.
  @throws InvalidSubnetException
  An invalid subnet identifier was specified.
  @sample AmazonElastiCache.ModifyCacheSubnetGroup
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/elasticache-2015-02-02/ModifyCacheSubnetGroup"
  target="_top">AWS API Documentation</a>