Long running EC2s with Cloudformation and ServiceCatalog

My organisation runs with a number of fairly tight controls for how we can build our environments. One of these is that infrastructure must be deployed via the service catalog using products that have been validated before being published for use. This means we rely on Cloudformation to build the EC2 servers we use.

My use case for EC2 is as long running compute nodes within a cluster that store data. This requirement comes from the software in use. This means they are not sacrificial like a web server or app server might be.

As such using autoscaling groups for the EC2s is not ideal, as I don't want the EC2s being terminated unexpectedly as this can cause data loss, and also new nodes need to be configured into the cluster which would mean a loss of capacity.

What I'm looking for is suggestions on how to manage the EC2s using Cfn and ServiceCatalog without having to push new versions of the Service Catalog products when we want to make changes to the EC2s, such as volume sizes, or instance types. One option could be custom macros and various lambdas but this gets complex quickly.

Terraform works well for this but is not an option due to the restrictions I mention around service catalog.

TIA....