Use CloudFormation Converter CLI Tool
This article gives the steps to use the CloudFormation Converter Command Line tool to converter AWS CloudFormation Templates from JSON to YAML or YAML to JSON.
So, basically you can take all those old JSON CloudFormation Templates and convert them over to the new YAML supported versions!
Follow the instructions and examples in the project README.md
I don't want to duplicate the instructions, just wanted another way to find the project to be more helpful.