Jackzo: Here is the gist of it:

1) Vendors no longer provide useless white items.
2) Vendors will give you fewer stacks of crafting materials, but the stacks are larger.
3) Vendors will give you fewer items overall, but you will see a higher incidence of higher quality items--more purple and magenta items, for instance.
4) Books now appear multiple per stack, but the stack will only replenish if you clear it completely from the vendor's inventory, and this will occur on an inventory reset governed by the conditions that you describe. So, if you have a stack of 5 books and you buy one, you will see 4 books, and this will continue until you buy all 5.

How does this affect killing NPCs? The Witchcraft Rogue trader in the 1st town when killed drops all of her books but no gold. In your mod however, she drops 5 of each book if all are replenished which means that you can get loads of gold? Also, what level do the 1st towns shopkeepers get new books for sale? I'm level 9 at the moment and was wondering when I can expect new spells outside of crafting them myself. Thanks a bunch

Sorry for the delay, I've been busy recently.

There's no change to how killing NPCs works, as it's not really something I can change. So yes, you can kill early NPCs for a nice gold infusion, but you will then have one less vendor to farm for powerful items throughout the game.

Vendor book offerings will (mostly) never change. You can always access the entire repertoire of spells by checking the book vendors of Cyseal, Silverglen, and Homestead.

To clarify, books are always restocked to a stack of 5, even if they are not completely bought out. This was one of the major changes we implemented to prevent the dreaded "out of handles" showstopper crash, and I'm proud to say that this particular change saves the use of thousands of handles throughout a playthrough.

So shopkeepers never get new books just update existing ones if you buy them? Thanks a bunch for the info