Aesthetics? Most certainly, although TexMod nullifies the need to actually change any files.
Quarian Female Engineer and Infiltrator "Tali", fashioned after the default Tali outfit modified to work on the MP model:

Geth Trooper Soldier and Infiltrator "Pyro", much lower specular levels to mimic the real Pyro as well as much fewer lights and some other changes:

Turian Soldier and Sentinel "Nihlus", familiar from ME1 with face paint and an approximation of the armor:

Batarian (all) "Blue Sun", also with accompanying pattern on the Blade Armor:

Asari (all except Justicar) "Shiala", approximation and removal of a lot of lights and some other minor cosmetic changes to all maps:

Asari (all except Justicar) "Omega", inspired by Aria's outfit, no lights and Liara's face texture:

Asari Justicar "Liara", almost unnoticeable hue and specular work to mimic Liara's alternate armor:

N7 Fury "Kasumi", Kasumi's loyalty outfit with embossed Spectre-logo and some minor cosmetic changes (vertical eye-slits instead of round lights):

Krogan Soldier and Sentinel "Blood Pack", the Skull and Fist doesn't really fit well on this model and is obscured by the Sentinel's tech armor:

Human Infiltrator and Engineer "Shepard", a Shepard-esque look for the basic humans:

Plus a host of other minor cosmetic texture changes, no more white plasticky-looking weapon attachments and so on.
Z.