Currently rewatching charmed and I just got to season 6. I understand that the Stillman sisters were able to touch the book by taking the charmed ones identities. However, up until this point, there have been several rules the show established surrounding the book of shadows.

1. Evil magical beings can’t touch the book.
2. If the sisters turn evil, the book turns evil.
3. Non-magical beings can touch the book (as we’ve seen with Glen when he was holding the book with Paige in S4 E11–Trial By Magic)

After the Stillman’s steal their identities, but prior to stealing their powers, the sisters can no longer touch the book. Why? They’re still good magical beings, they should be able to regardless of their missing identities.

The stillman’s are then able to touch the book in order to find the spell to take their powers. But if the book is linked to their powers, and is still the good version of the book, then why does it let evil touch it? (This one, I can give more leeway to because of the identity theft spell but it still seems slightly contradictory to the previous rules since the good beings that have the charmed powers the book is linked to are unable to touch it).

Once their powers are stolen, why isn’t the book immediately influenced by the new evil charmed ones/stillman sisters? We see that the powers stop working once their bond is severed, showing the book and the powers are intertwined.

I know the simple answer boils down to writing, but does anyone maybe have an in-universe explanation for some of these?