I've came across this 2 year old question in Stack Overflow, I'm starting a side project at work to explore the potential of Cardano.
There is an old documentation page that mentions cardano-sl component which has been currently decomposed into several others.
This other page(https://developers.cardano.org/docs/get-started/running-cardano), reads:
Alternatively, you can spin up your own custom Cardano network, but that is outside the scope of this guide.
Bottom line the question is whether it is possible to create custom private Cardano networks besides the mainnet and testnet networks, and if so, where can we find documentation about that process.