Kly, you can indeed replace the soldier clothing with the Sith Uniform model...
  It is also something easy to do... and a prefect intro mod. ;) 
 1. Fire up KT... KOTOR Tool available here. (
http://kotortool.home.comcast.net/index.html) 
 2. Look in BIF's/models.bif/Aurora Model for n_sithcomm.mdl and n_sithcomf.mdl extract these and save these to a new folder. Look in BIF's/models.bif/mdx for n_sithcomm.mdx and n_sithcomf.mdx extract these and save these to the same new folder. 
 3. Look in ERF's/Texture Packs/swpc_tex_tpa/N for N_SithComF01.tpc, N_SithComF02.tpc, and N_SithComF03.tpc and N_SithComM01.tpc, N_SithComM02.tpc, and N_SithComM03.tpc. You double click on these files and the Texture window opens click write file and save these 6 textures to your new folder. 
 4. Ok, now rename the mdl and mdx files like so...  
 > n_sithcomf.mdl to PFBBL.mdl
 > n_sithcomf.mdx to PFBBL.mdx
 > n_sithcomm.mdl to PMBBL.mdl
 > n_sithcomm.mdx to PMBBL.mdx 
 5. Ok, now rename the texture tga files like so  
 > N_SithComF01.tga to PFBBL01.tga
 > N_SithComF02.tga to PFBBL02.tga
 > N_SithComF03.tga to PFBBL03.tga
 > N_SithComM01.tga to PMBBL01.tga
 > N_SithComM02.tga to PMBBL02.tga
 > N_SithComM03.tga to PMBBL03.tga 
 This will give you 3 different clothing variants too, you can wear them by using the giveitem cheat for g_i_clothes01 through g_i_clothes03 if I'm not mistaken. 
 6. Put the 2 mdl and 2 mdx and 6 tga files in your override and start a game with a Soldier PC and put on some clothes and you should have a Sith uniform.  
 I hope this helps! :D