I wouldn't even try to merge a new version into ours, since the differences are huge. Other techniques work better, like for instance cherry-picking certain commits we want to include in our fork and solving conflicts per commit.

So my opinion is that we should sanitize the existing code, since it's now in our responsibility. Sure, it's not a big deal to revert those small formatting changes, but I'd prefer to generally sanitize our code whenever we can. PEP-ifying the code it not a big deal, one sees the diffs immediately, as opposed to the semantic / functional changes we already introduced.