The values that can be set in the appSettings.json are all from classes Suffixed with "Options" at the end. I did a search and found

namespace EPiServer.Licensing
{
  public class LicensingOptions
  {
    public const string DefaultLicenseFile = "License.config";

    public string LicenseFilePath { get; set; } = "License.config";

    public string LicenseKeySignature { get; set; }

    public string LicenseKey { get; set; }
  }
}

So if think something like

{
  "EPiServer": {
      "Licensing": {
        "LicensingOptions": {
            "LicenseFilePath": "PATH"
            }
        }
    }
}

Might work but I've not testing it, but all Options classes SHOULD be settable.

It could also be just Licensing instead of LicensingOptions in that lower object

Thanks Scott!

I'll test it.

This came up once before on the forums -- in that thread, the answer they came up with was:

"EPiServer": {
    "CMS": {
      "LicensePath": {
        "Path": "./License.Staging.config"