Alter default header/footer in WINDOW mode when printing to pdf

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Alter the default header/footer when printing to PDF

, but im trying to alter the default header and footer in window mode. Specifically, I want to edit the date section. I found

https://github.com/chromium/chromium/blob/master/chrome/browser/resources/print_preview/data/model.ts

to be the source code of chromium, but it seems the only supported argument i can pass is isHeaderFooterEnabled, which is a boolean.