I recently learned about Helmfile's support for deep declarative patching of rendered charts, without requiring full forks with value-template-wiring. It's been a gamechanger!

https://helmfile.readthedocs.io/en/latest/advanced-features/...

In your context, it might help certain clients. It does require that the upstream commit to not changing its architecture, but if the upstream is primarily bumping versions and adding backwards-compatible features, and if you document all the patches you're recommending in the wild, it might be an effective tool.