player_xp_multiplier is xp multiplier you gain by killing an enemy.
hero_xp_multiplier is xp multiplier your heroes gain by killing an enemy.
regulars_xp_multiplier is xp multiplier your troops gain by killing an enemy.
The most amount can be 10 (or 15, I have never tried).
If your module.ini don't have these lines, you can add these lines to anywhere in your module.ini. These lines are in Viking Conquest mod's module.ini though.
skill_points_per_level is the skill points you will gain when you level up for 1 level.
attribute_points_per_level is the attribute points you will gain when you level up for 1 level.
Other things I have not tried yet.
Next you can modify skills.txt in each mod's folder.
The second number of each skill is the skill limit, you can adjust them to 15. Note: The max number is 15, you shouldn't increase the skill limit above 15 or the skill level will return to 0 after upgrading your skill when your skill is already lv15.