If you can select a slave, go to Customization, and find a button for "Random Portrait", then the mod is successfully applied. The most likely problem for applying this mod is that thanks to recent improvements the game can recognize the location of the mod better than the mod can adapt to changes in location. So it is important that the path to the info file be exactly ".../Strive/mods/randomportraits/info.txt", any differences can cause the mod to fail (unless you have assigned a new folder for mods, in which case replace the first 2 levels with that).
Note, his mod does not come with any images, so you need to download a compatible image pack. Most image packs are compatible with the mod, though they tend to be for the pre-1.0 races (before Dark Elves became Tribal Elves, and Drow became Dark Elves). It is usually fairly straight-forward to rename the race folders to switch to the 1.0 races.