You can still do this, this file however will only be created if you are utilizing the non default rust loot tables. Enable it in one container and you will be able to find the file under data/MagicLoot/Rarities. In here there is a full item list sorted in each of its rust rarity. You can in there then disable certain item spawns - this however will only apply for the custom loot tables. If you want to blacklist specific items for the default rust loot tables you will need to manually add them to the blacklisted item list.

I was considering if I should remain doing it like it was before but ended up having a few reasons against that.

1. First performance, the way its working atm is that it gets removed on plugin load from the custom item pool a random item gets selected from.
This means that a loop over the items in the end becomes redundant and also removes the possibility of retrying if say an item is selected but not marked spawnable (because it is not in pool of items to begin with)

2. The default rust loot tables are rather simple and items that are not wanted can be blacklisted fairly easily and should, most of the time, not consist of many.

Before the update i would use the custom stack sizes to limit the amount you can get from a crate for example 20 c4 at maximum from a crate , whilst the stacksize for c4 is 500 with stacksizecontroller. 

But now it doesnt work anymore and with the same mulitplier as before the update the c4 goes up to 160 in a crate even when i am capping it at 10 with the magicloot stacksizes.