I picked up a White Dwarf containing a nifty Slaughterpriest a few months back, but didn't have any particular plans for him until last month.
For a few years now the Corvallis wargaming club has done a Secret Santa mini exchange, where participants draw a name, and paint a mini for that person's army (usually an HQ or similar). I drew a buddy who played renegade IG who uses AOS Chaos marauders as troopers, so I decided to turn the White Dwarf mini into a commander. (sorry for the image quality, I didn't have time to take a proper picture before I wrapped him up)
I didn't change too terribly much about the original mini.
* Head swap with a Blood Angel (trimmed away the hair & modeled on a mohawk-ish haircut)
* Weapon swap with plasma pistol
* Left off the loincloth, so I added a Khorne bit from Khorne Bloodcrushers to cover some divets in the armor.
* Replaced a skull-totem thing in his back with a Chaos Icon (from a chaos vehicle sprue, I think)
* Modeled a daemonic face onto his flail
The hardest part was probably finding the right head. The mini is a lot bigger than you'd expect (at least a head bigger than an AOS Eternal), so scale was an issue. Fortunately I've been collecting various heads for Deathwatch minis & one of them fit the bill nicely. Hope you enjoy.