duaryn you meanie...this thread has been unanswered for months now.
I'm sure duaryn has found a way to change the MP texture by editing the properties in the Unreal Editor under objects. I'm not going to even attempt to locate what he found as it's really not something I excel in.
Here's an easier way to make the Boss texture appear in MP.
Before you do anything please make a backup copy of your CloneTextures package located C:\Program Files\LucasArts\Star Wars Republic Commando\GameData\Textures
As RC has overlooked the Boss skin and hardcoded the skins we can select I went about adding the Boss texture by simply renaming it to a file that the engine recognises. We're going to lose the green commando here but that skin's not the greatest anyway.
Open the editor > Go to textures > Select Clone Textures (sub heading) CloneTextures > Go to Texture CloneCommado38 > Right click and click Export to File... > Save as CloneCommando40.bmp
Please add the extension .bmp or you won't be able to save the file.
Let's bring the Boss file back in now. In the Textures area again go to File > Import > Select the saves CloneCommando40.bmp and OK > In the Import Texture window click OK. Scroll down to CloneCommando40 and the green skin will have been replaced with the Boss skin.
Exit the Unreal Editor and OK when the prompt appears to update the Clone Texture Package.
Now start Republic Commando and go to Multiplayer > Customize. Select the Ranger skin and the Boss skin will appear.
Host your own MP map and either kill yourself or ~ to open the console and type togglebehindview
You'll have to do some quick turns to see the skin in all of its glory or ask someone else to make the same edits so you can play together. Once you've made this change you won't be able to enter anybody elses server unless they have also made the same edits to their texture package. Republic Commando is running on a heavily stripped down version of the Unreal Engine and we've lost a lot of the functions and flexibility found in other Unreal based games.
When you're ready to restore the texture simply delete the edited CloneTexture package and replace it with the original backup.
Anyway, here are a few screenies of a map I finished today called Wook.
http://rc.injapan.org/images/arramus/boss.jpg)
http://rc.injapan.org/images/arramus/boss1.jpg)
http://rc.injapan.org/images/arramus/boss2.jpg)