In 4.19 both this install method and the clusters created by it will be considered Tech Preview. We need to flag the installed clusters with TechPreviewNoUpgrade to ensure they cannot be accidentally used in production. The place it makes most sense to set this is in the UI code (note that this should be unconditional; there is no user interface to turn it on or off).

The mechanism to do this through the assisted API is to set an install-config override with:

{"featureSet": "TechPreviewNoUpgrade"}