So the change in regulation happened in 2020. How then does this hypothesis explain changes in ocean temperature before then? What is the relative magnitude of the correction vs CO2-only-based models?
It doesn't. This model isn't an alternative to CO2 based atmospheric warming models, it just explains a very recent trend in ocean temperature. This branched off a discussion about recent temperature trends. Everyone asking questions about general long term trends either aren't reading or are starting a different conversation.
GP explicitly referenced this phenomenon in an unqualified manner when addressing ocean warming. If they wanted to be understood the first time, they should have clarified the context.