What if the paper of my drawing changes at the last moment?

I have a full set of about 500 drawings sheets, in Autodesk AutoCAD 2018, with layouts, paper sizes and scales set up for an A0 paper, meant to be printed in A0 at the project beginning.

At the very end of the project, at the moment of the final deliverables, the client requested us to print everything in A1 paper. Now, printing in A0 is not as option.

Which should be the optimal resource and political way for solving this dispute?

1. Should we change ALL but not EVERYTHING in the drawings, keeping the A0 Layouts, keeping all the viewport scales, and changing the scales texts, e.g. 1:5000, multipling them by $sqrt 2$ (A0/A1 ratio), and having awful scales like 1:7070, or better looking and somehow approximate figures such as 1:7000 in this case (among other figures), and changing the revision of ALL the drawings?
2. Should we absolutely change ALL and COMPLETELY the viewports, for fitting the new scales, in this case, 1:7000, changing the Layout to A0, changing the scale texts, and changing the revision of ALL the drawings?
3. Should we tie a clean template note "All Scales for A0 Paper" in ALL the drawings, leaving everything untouched, indicating the scales are for A0 paper, and changing the revision of ALL the drawings? Or leaving all revision as is, excusing the change is only in the template?
4. Should we leave ALL the drawings untouched, not requiring any additional approvals, nor revision upgrades, and changing only the Global Index Sheets of the overall set, with a clear note "All Scales for A0 Paper"?

Whatever the automation of annotations indicating the scale, passing from A0 to A1 will lead to nasty scales, e.g. from 1:5000 to 1:7070 (!), hence this do not seems to be an automation problem… Unless there could be a way to "round" scales at a viewport, which is a completely different topic…

Note. Please keep the discussion technical; how, when and why to charge the client is a discussion out of the question.