[tka]

This should work just fine. Carrion Centaur now needs 1N1D caster and 3 nature gems. The spell is also specific for Pangaea now.

#selectspell "Carrion Centaur"
#school -2
#researchlevel 10
#path 0 6
#path 1 5
#pathlevel 0 1
#pathlevel 1 1
#fatiguecost 300
#end

If #school is set to -2 you must specify the nation with #researchlevel X -command where X defines the nation.