Warlocks can customize their pets in the Barber Shop in Patch 10.1.5 and here’s a preview of all available pet customization options.
Imp Customization Options in Patch 10.1.5
Source: Terestian Illhoof
Source: Burning Crusade Timewalking
Source: Legion Time Rifts
Source: Grimoire of the Fel Imp
Source: Default
Source: Found at the Faire
Source: Pusillin
Source: Matron Folnuna
Source: Vi’el
Source: Imp Mother Dyala
Source: Legion Timewalking
Source: Class Quest
Source: Class Quest
Source: Class Quest
Source: Class Quest
Felhunter Customization Options in Patch 10.1.5
Source: Default
Source: Legion Time Rifts
Source: Felhounds of Sargeras
Source: Unknown
Source: Unknown
Voidwalker Customization Options in Patch 10.1.5
Doomguard Customization Options in Patch 10.1.5
Succubus Customization Options in Patch 10.1.5