Here is a list of all the parameters that you can change in-game.

Global parameters :
Time interval between the two shouts/ spells
Number of spectators
Enemy intimidation
Music

NPC Parameters:
Activate / Deactivate duels versus NPCs
Chances of starting a duel
XP multiplier
Speed multiplier
Difficulty multiplier
Damage multiplier
Level influence
Skill influence
Advantage (two handed spells / staffs)
Magicka gauge
Overdrive Gauge
Finishing Moves
First person duels
First person finishing moves

Dragon Duel Parameters:
Activate / Deactivate duels versus Dragons
Chances of starting a dragon duel
XP multiplier
Difficulty multiplier
First person duels

Modifiable hotkeys :
Left click
Right click
Overdrive
Debug