I have a CFN stack for my VPC where I first create only public and private subnets, which get assigned default CIDR blocks. Now after a while I need to add isolated subnets to the VPC as well. When I try to update the CFN stack, I get an exception – "The CIDR '10.0.0.0/25' conflicts with another subnet

Is it possible to reassign the CIDR blocks to the subnets after adding more subnets in CFN stack update?

Here’s sample code:

    if (<some condition>){
        this.createVpcWithIsolatedSubnets();
    } else {
        this.createVpc() 
    }

createVpc() {
    const vpc = new ec2.Vpc(this, `VPC`, {
        maxAzs: MAX_AZ,
        subnetConfiguration: [
           {
               name: 'Public',
               subnetType: ec2.SubnetType.PUBLIC
           },
           {
               name: 'Private',
               subnetType: ec2.SubnetType.PRIVATE_WITH_EGRESS
           }
        ]      
   });
}

createVpcWithIsolatedSubnets() {
            
    const vpc = new ec2.Vpc(this, `VPC`, {
        maxAzs: MAX_AZ,
        subnetConfiguration: [
           {
               name: 'Public',
               subnetType: ec2.SubnetType.PUBLIC
           },
           {
               name: 'Private',
               subnetType: ec2.SubnetType.PRIVATE_WITH_EGRESS
           },
           {
               name: 'Isolated',
               subnetType: ec2.SubnetType.PRIVATE_ISOLATED
           }
        ]      
   });
}