Noob wants to change drop chances and leveled items

There are mods here in the download sections in cheats and balancers that do something like what you are asking for. Have a look.

If you want to mod the drop rates yourself have a look in the files in the world/contentdb/pcontent/macros folder found in Logic.ds2res in the DS2 resources folder (or xLogic.ds2res for the Broken World addon). Specifically pcontent.gas

Here's some code from pcontent.gas that applies to the chance for items from chests in DS2.

[chest_container_macro]
{
	[oneof*]
	{
		[all*]		// 1 modifier magic item
		{
			chance = 0.5;
			il_main = #/-mod(1);
			pcontent_min_level = #item_level - 5;
			pcontent_max_level = #item_level + 2;
			max = 1;
			min = 1;
		}
		[all*]		// 2 modifier magic item
		{
			chance = 0.46;
			il_main = #/-mod(2);
			pcontent_min_level = #item_level - 5;
			pcontent_max_level = #item_level + 2;
			max = 1;
			min = 1;
		}
		[all*]		// rare item
		{
			chance = 0.025 * (1 + (#magic_find * .01));
			il_main = #/-rare;
			pcontent_min_level = #item_level - 3;
			pcontent_max_level = #item_level + 2;
		}
		[all*]		// unique item
		{
			chance = 0.0075 * (1 + (#magic_find * .01));
			il_main = #/-unique;
			pcontent_min_level = #item_level - 30;
			pcontent_max_level = #item_level + 2;
		}
		[all*]		// set item
		{
			chance = 0.0075 * (1 + (#magic_find * .01));
			il_main = #/-set;
			pcontent_min_level = #item_level - 50;
			pcontent_max_level = #item_level + 2;
		}
	}
}

Shops are a little trickier as I believe they are meant to sell trash. I don't think you can do much about the randomized items that the shops can potentially sell but you can make a shop sell crafted or unique items by defining their template name in shops.gas found in the maps info folder (world/maps/map name/info). Have a look at the BWSuper Shops mod, which adds all unique/set items for sale in Act I and Act II shops.

Guru's RenownChance in the Downloads section is a mod that gives a flat +%15 chance for rare/unique/set item drops

Thank you guys very much, especially for the kind and detailed information about editing the pcontent.gas! This is very interesting!! So you sad, the items found in the chests must always add up to 100% chance - this means I can't set up the magical items to appear even less, right?

My intention was to make the find of magical items more seltdom and to add up more nice items to the shops so you have got a bit more from your collected gold coins. This is were your idea about this BWSuper Shops mod perfectly fits in at least!

I don't have the game installed right now as I recently formated my HDD but just to be sure: Can I just open and extract the .ds2res file with my winrar? I know there was a special software for the ds2res files too but I recall this didn't work for Win7 64bit if I remember correctly.

Hopefully you will read this and show me one or more of your great tricks to solve my problem. I really honour you guys for helping me out that much!

Thanks to KillerGremal I now have even more variables to play with:

'Normal' magical (2 modifiers):
il_main = #/-mod(2);

without magic (enchantable sometimes):
il_main = #/-mod(0);

This is very cool, so now I can even edit what the monsters drop!

The editing of the drop rates works good for me now, but how exactly can I edit the shop templates? I extracted the logic.ds2res but there's no shops.gas in there! o_O

Where is the shops.gas located and does someone have a tip where to look in the file to give selled items generally a higher level. (I am Level 40 and the shops still sell Level 1 items)

the shops.gas file is stored inside the map file. u have to open the .ds2map file for whatever map's shop that u want to modify.