These lines go into your ThMutators.ini file (these are the default values):

[ThMMsFBs.MMMsFBs]
AirborneLightRad=1
bAdvancedPOD=True
bDamageIgnoreWall=False
bExcludeButtons=False
bFCGuardFrob=False
bFCThiefFrob=True
bPushIgnoreWall=False
bWaterExplo=False
ExpDamageRadius=200
ExpFlames=0
ExpIgniteRadius=20
ExpLightRad=10
ExplosionDamage=80
ExplosionPush=400
ExpPushRadius=200
ExpRelightRadius=100
FCMaxDensity=1.250000
FCSpawnTime=10


What they do:
(note that booleans can be True or False, Integers any natural number, and floats any decimal number)

AirborneLightRad
-  Integer. Radius of the light that a firebolt/firearrow has while flying through the air. Use 0 to disable airborne light.

bAdvancedPOD
-  Boolean. When True, proximity is determined from a point on the collision cylinder instead of the center of the object. Essentially it means that direct hits deal full ExplosionDamage and ExplosionPush.

bDamageIgnoreWall
-  Boolean. Applies damage, torch relighting and player burnination through walls only when set to True.

bExcludeButtons
-  Boolean. When se to true, no ThPushButtons are pushed.

bFCGuardFrob
-  Boolean. When set to true, firechrystals are frobbable by guards.

bFCThiefFrob
-  Same as above, but for thieves.

bPushIgnoreWall
- Same as bDamageIgnoreWall, but for explosion push.

bWaterExplo
- Boolean. When set to True, firebolts explode with a neat bubble effect when they hit something in water.

ExpDamageRadius
-  Integer. When above 0 it sets the max damage radius (in UUs) for damage, when 0 or below, it turns damage off.

ExpFlames
-  Integer. Number of flames to be spawned upon explosion.

ExpIgniteRadius
-  Integer. The max radius at which to set players on fire.

ExpLightRad
-  Integer. The radius of the explosion light. Use 0 to disable explosion light.

ExplosionDamage
-  Integer. The damage dealt at the centre of the explosion. The damage is faded linearly, and is 0 when distance equals ExpDamageRadius.

ExplosionPush
-  Integer. The velocity (in UUs) added to an object at the centre of the explosion. Like with damage, it is faded linearly.

ExpPushRadius
-  Integer. Same as ExpDamageRadius, but for explosion push instead.

ExpRelightRadius
-  Integer. The max radius at which to to relight torches.

FCMaxDensity
-  Float. The maximum density of firechrystals in the area of spawning. The density is measured by total number of firechrystals within a linearly faded radius. Basically, the higher the number, the more firechrystals can be spawned.

FCSpawnTime
-  Integer. Time in seconds between each attempt a firechrystal makes at spawning. There is no guarantee that a firechrystal spawns, as forcing it to do so might at worst cause infinite loops.