Tool for manipulating YAML files?

We want to implement a workflow that includes having YAML configuration files where we wish to change some of the contents before actually using them, and we are looking for a good command line tool to do this. This can be as simple as setting a target-specific value (like an URL) in an existing node, but preferably would be able to add or modify whole blocks of the YAML file. In a perfect world, I would like something as powerful as the axis in XSLT. We will use this with Maven in Docker files, where we prefer Debian-based images, but not a strict requirement.