Helm: Overwrite configuration from json files, is there a better way?

Question

We use helm to deploy a microservice on different systems.

Among other things, we have a ConfigMap template and of course a value file with the default values in the repo of the service. Some of these values are JSON and so far stored as JSON string:

apiVersion: v1
data:
  Configuration.json: {{ toYaml .Values.config | indent 4 }}
kind: ConfigMap
metadata:
  name: service-cm

config: |-
  {
    "val1": "key1",
    "val2": "key2"
  }

We also have a deployment repo where the different systems are defined. Here we overwrote the values with json strings as well.

Since the usability of these json strings is not so good, we want to move them to json files.

We use AKS and Azure Pipelines to deploy the service. We create the chart with:

helm chart save Chart $(acr.name).azurecr.io/$(acr.repo.name):$(BUILD_VERSION)

and push it with:

helm chart push $(acr.name).azurecr.io/$(acr.repo.name):$(BUILD_VERSION)

and upgrade after pull and export in another job:

helm upgrade --install --set image-name --wait -f demo-values.yaml service service-chart

What we have already done is to set the json config in the upgrade command with --set-file:

upgrade --install --set image-name --wait -f demo-values.yaml --set-file config=demo-config.json service service-chart

What works though only for the values, of the different systems, not for the default values. But we also want to outsource these and also do not want to do without them. Therefore at this point the first question, is there a way to inject the default values already per file, so that they are in the saved chart?

We know that you can read files in the templates with the following syntax:

  Configuration.json: |-
{{ .Files.Get "default-config.json" | indent 4 }}

But we can't override that. Another idea was to inject the path from the values:

 Configuration.json: |-
{{ .Files.Get (printf "%s" .Values.config.filename) | indent 4 }}

But the path seems to be relative to the chart folder. So there is no path to the deployment repo.

We now have the following solution with conditional templates:

data:
  {{ if .Values.config.overwrite }}
  Configuration.json: {{ toYaml .Values.config.value | indent 4 }}
  {{ else }}
  Configuration.json: |-
{{ .Files.Get "default-config" | indent 4 }}
  {{ end }}

In the deployment repo the value file then looks like this:

config:
  overwrite: true
  value: will_be_replaced_by_file_content

And demo-config.json is set with the upgrade command in the pipeline.

This works, but seems a bit fiddly to us. So the question: Do you know a better way?