scripting Need help scripting with globals

[Biovex]

I've been making a mod that adds a new land, people, weapons, spells etc, and I've been looking for a way to make a script that makes the player get more XP/skill points permanently after killing npcs with a certain keyword. So far I have the global variable and script setup to keep track of npcs killed that starts at 1.0 and goes up by 0.001 per npc, I just don't know how to take the modify skill use value and multiply it by the global variable. Basically I want to do the same as the picture below, taken from the rested perk, but multiply by the a fore mentioned Global variable instead of a set value, and I'd like to do it with a script instead of a perk entry.

https://imgur.com/a/kNeFY1P

 

Any help would be greatly appreciated.