I found out how to do this. First off, open your user.ini file, and check for the part that looks something like this:

• [DefaultPlayer]
  Name=Chruser
  class=BotPack.TFemale1
  team=0
  Voice=BotPack.VoiceFemaleOne
  OverrideClass=
  AutoReload=True
  HideCrosshairs=False
  HQVoices=True
  Skin=FCommandoSkins.cmdo
  Face=FCommandoSkins.ivana

Change that to:

• [DefaultPlayer]
  Name=Chruser
  class=BotPack.TFemale1
  team=0
  Voice=BotPack.VoiceFemaleOne
  OverrideClass=
  AutoReload=True
  HideCrosshairs=False
  HQVoices=True
  Skin=Botpack.Skins.IntroDude
  Face=

In short, you should remove what's after Face= and change the Skin= part to something else (I guarantee you'll laugh if you do it like I did here).
Well, take your time, and do some testing in unrealed if you want some mad skins. If someone finds out how to use a transparent one, you can always let me know

"Stephen Wolfram is the creator of Mathematica and is widely regarded as the most important innovator in scientific and technical computing today." - Stephen Wolfram