With the existing labels for CPython PRs, I think a type-behavior label could be quite useful for describing PRs that involve changes in functionality and don't add new features (which would be covered by type-enhancement). This label already exists on BPO, and frequently feels missing on GitHub. It may not seem incredibly important at the moment, but I think it will be more noticeable as we transition to GitHub issues.

As a concrete example of a PR that it would be well suited towards, I recently opened a PR that makes an internal change in concurrent.futures to not use daemon threads for compatibility with subinterpreters. A type-behavior label would definitely be appropriate, while none of the others would quite fit.

I can also think of quite a few other types of PRs that it could be well suited towards, such as new warnings (including deprecation, resource, etc), removals, and any other code changes in the internals that wouldn't qualify as a bug fix, performance optimization, or enhancement.

The addition of the label should be rather straightforward, as it would not include any new functionality or act as a trigger for a bot action.