Blacklist still doesn't work. How do I do this?

"BlacklistedSkinList": {
"4124294": true,
"124124924": true,
"1174053561": true,
"1869420706": true,
"2466777271": true,
"1818358695": true,
"2362316408": true,
"645187315": true,
"815064512": true,
"811728306": true,
"1533598443": true,
"809693916": true,
"820427049": true,
"2628823067": true,
"871402683": true,
"2358885526": true,
"1192971478": true,
"2269724963": true,
"2424485558": true,
"1962030495": true,
"2101133226": true,
"1707369274": true,
"2360592677": true,
"2490406124": true
},

2101133226 Skin M249 is still exposed in the shop.

Which GUI page are you seeing it?  (blacklist does not block skins you already own on the "My Skins" page)

To be precise, I'm using ChaosMod's SkinPerks plugin.

This is a plugin that gives various properties to skins. I don't want to make it easy for users to get skins with this trait. So I need an exclusion from the skin store.

I added a blacklist but nothing happened.
It is still available for purchase in the M249 category, and is being shown to people.

I don't seem to be able to replicate this, when i add your config then 2101133226 no longer shows in the category.  I will put this on hold for now until i can replicate it.