Extending existing resource with custom fields

I’ve looked at Convert from JSON to an F# anonymous record and Migrating to IArmResource, and (correct me if I am wrong) it looks like it does not allow adding fields/properties to existing resources (but rather only creating new resources from scratch). Is there a way to just add custom JSON or anonymous record to e.g. a webApp?

More specifically I am looking to mount Azure Storage as a local share in a container app in App Service by adding the following under “properties” (next to e.g. siteConfig that is already generated by Farmer):

"azureStorageAccounts": {
    "my-storage-mount": {
        "type": "AzureFiles",
        "accountName": "storageAccountName",
        "shareName": "sharename",
        "mountPath": "/data",
        "accessKey": "..."
    }
}

Would I have to recreate the whole webApp or Microsoft.Web/sites/config JSON manually in order to add this section, or is there a way to just “jack in” a custom field for azureStorageAccounts?

[isaacabraham]

@Yakimych exactly right. We’d have to have some way of splicing the JSON together. A crude option would be that we give you access to the final JSON as a JObject (or whatever the System Text JSON equivalent of that is) and it’s your responsibility to return back some valid JSON.

[isaacabraham]

@Yakimych great question. For the moment, it’s unfortunately the former - you can only add in entirely new resources, rather than modifying an object. I’ve been thinking about ways of letting you “plug in” to the very bottom of the pipeline though to modify the JSON that is output as well, but unfortunately nothing that’s ready for testing out.