You could alter this setting
# Prevent players from acquiring these mobs as a morph.
# Leave blank to allow acquisition of all compatible mobs.
# Formatting is as follows: <class>, <class>, <class>
# Example: am2.entities.EntityBattleChicken, biomesoplenty.entities.EntityJungleSpider, thaumcraft.common.entities.monster.EntityWisp
S:blacklistedMobs=
or
# Disable the flight ability until a player has reached the nether?
# 0 = No
# 1 = Yes
I:disableEarlyGameFlight=1