To reskin 38's HudArms: Open the Texture Browser. In the drop down menu select:
HudArmsTextures>HudArms. There you will find a texture named HudArms. Just plain HudArms. And also a texture named HudArmsWhite_Shader. Rename that to HudArms.
I think that's how you do it.
The more complicated way is with GIMP. Take a screen shot of the HudArmsWhite_Shader. (alt+prt scr/sysrq) Paste it into gimp. Choose the selct tool and select the picture of the hudarmswhite_shader. Now scale it to 512x512. Copy it, and then create a new GIMP Picture, that is 512x512. Now click CTL+V.(Paste) Save the picture of the 512x512 HudArmsWhite_Shader as a .TGA(TarGa), and name it "HudArms" (without the quotes). Now go back to unrealed where you first took the picture of the HudArms. Click File>Import. Find you HudArms TGA, and click open. In the name thing, type HudArms if you haven't saved your picture with that name. Make the MIPS 2. Now click OK. If you have done this correctley, 38's HudArms should now be white/chrome. I hope I helped.
Sandcrawler covered changing AIs' weapons, http://http://www.sandcrawler.net/forum/rcmod.php?page=tutorial-21