Yes but best way to do is :
You have steam version all good , but download the full game from taleworlds ( 555Mbytes about ) .
Install it , then you have a " real " Mount&Blade Warband folders on /C: programs files .
Since you have Steam version with CD key already register , your " other " M&B will work without asking anything .
If you want play mods , just install it on Talewords one , and launch it .
I have myself Steam version ( i launch it's from Steam page and not from desktop ) . And the version from Talewords , have a shortcut on desktop .
Just remind , Steam auto update the game version . So don't forgot to update your talworlds one by the website manually . Both of your game will use 9 savegames , they are comon , you play Steam one or Talewords one = same savegames . But if you have 1 at version 1.125 and other at 1.123 for exemple , this can corrupt your savegame if you start play with 1.125 then load it with 1.123 version .