1. I made sure to turn off the automatic updates in the properties of the game on steam.
2. I went to program files, clicked on steam, steamapps, and then common.
3. I right clicked on mount and blade warband and went to the properties.
4. I clicked on the previous versions tab and selected an option prior to the update.
5. I moved that version to my desktop, deleted the previous one and replaced it with the older version by dropping it in the common folder.
I don't know how far back your previous version is, but this worked for me.