That isn't an installation issue, that's something we didn't fix from original Rome: Total War.
The issue is that portraits in RTW are attached to cultures, not factions, so if we'd changed portraits:
- Kislev, both Empire, and Brets would have shared (kinda works)
- Lizardmen would've got their own (only one that really works well)
- The 3 elf factions would've shared (barely works given how different the 3 factions are for skin tones etc)
- Araby and Tomb Kings (doesn't work)
- Dwarfs, Vampire Counts, Chaos Dwarfs, Luccini would've shared (and now the problem really becomes apparent)
- Orcs, Skaven, Chaos, Ogres, Dragon Islanders, Beastmen (Yeah.)
We could've put some generic thing in that wasn't a face, but we decided whilst testing that it was better to still have a portrait so you could tell who was who, even if the portraits were all wrong for species etc. Hope that explains it, and really glad you're enjoying the mod.