Futuza

Personally, I wouldn't recommend depriving yourself of the fun experience of beating the game the way it was designed to be, but if you insist you could do a couple of things to make Desaan a wimp.
The most straight forward to what you're asking is to edit his npc file.  You can find a tutorial about how to do this here (note might vary slighty as this is for JKA not Outcast, but its basically the same format):
  Note, that you probably want to make a seperate pk3 to store the modified Desaan .npc in, so as to not overwrite the original gamefiles permanently.  The easiest way to make him a scrub is change his health value to 1hp, but have fun trying out all the new stuff.  You could change his class, or lower his accuracy, aggression, etc.  Keep in mind doing this will probably mess up your save file, so don't mod until you have a backup save.

Making new weapons works basically the same as it does with base.
 
Multi-player: https://jkhub.org/tutorials/article/131-how-to-create-a-new-weapon-mp/
 
Single-player: https://jkhub.org/tutorials/article/203-adding-a-new-weapon-single-player-game/

There are quite a number of skinning tutorials here: http://jkhub.org/tutorials/category/7-skinning/
 
Such as Omnicron's or Mug's or Milamber's

Okay I figured it out, I should have waited one more minute to discover the answer...  
 
"https://dl.dropboxusercontent.com/s/3fb4i41rek8eg6l/ERw2LuU6Jj8.swf"
 
So change the "www.dropbox.com" part of the url to "dl.dropboxuercontent.com".

Don't forget that Steam is DRM software.  It inherits evil as a result of its nature.
 
The only way to not update is to keep steam from connecting to the internet.  Source.

Which version of internet explorer are you using?
Have you tried using using internet explorer with add-ons disabled?  (Windows Key + R” then Type “iexplore –extoff)
Have you reset to factory settings?  (tools > internet options > advanced > Reset...)

If that still doesn't work you can always try making a bat file that says:
 
jasp.exe + g_saberMoreRealistic 1