i got tired of having to try to extract the same infusion 2-5 times and spending +5k silver just so i can have blunt on my favorite weapon. so here is the location of the folder you need to modify if you want to set your own infusion extraction chaces

C:\Program Files (x86)\Steam\steamapps\workshop\content\294100\2063008864\1.5\Base\Defs\Tiers