Are you launching via the CloudFormation console or the AWS CLI tool?
You shouldn’t need to edit the template directly, if you’re launching through the console then you can provide the values as described in my previous response.
If you’re launching with the AWS CLI tool then you can supply the feature parameters as follows:
--parameters FlightFeatures='configure-docker ellexusmistral ansys-fluent-v170'
Once the stack has been created, you can verify the installed features by running:
alces customize list
And to see features available for install, run:
alces customize avail