Thank you so much for taking the time to write this article twice (English and Italian), and then making the effort to get it out of moderation-lock :)
It was an interesting read, it shows how really deep you went in the machine internals to reach your goal (including learning a bit of Assembly!).
That's very honourable of you, especially considering that the C64 wasn't the only machine you were developing for!
The solution you ended up using could be overkill, and also limiting since you're sacrificing quite a bit of RAM just for the purpose. There's another trick (that I haven't tested yet, alas) in one of the old C64 books, "Mastering Machine Code on your Commodore 64", that involves modifying a 1D table kept in lower RAM and used by the KERNAL; it's still about modifying one byte in there, but without having to copy anything from ROM.
In that case, it explains how to scroll one line down but, as far as I understand it, it should be even easier to scroll up.
Since the book has been recently republished, it's a bit hard to find: here's the italian translation of it, the trick is described on the right page towards the bottom.
The original English book can still be found on commodore.bombjack.org, under C64/Books.
If you're curious, I can update you once I manage to test & understand that trick myself (as I'm going to need it for my next project, wink wink, nudge nudge :)