I have used the following on my server( all 4 cells) and after several wild dino wipes, I am not seeing any more alphas.... i'm not saying this has worked, but so far it seems to be working... lol. i'll keep you updated if i do see any alphas.
[/script/shootergame.shootergamemode]
NPCReplacements=(FromClassName="MegaWolf_Character_BP_C",ToClassName="")
NPCReplacements=(FromClassName="MegaLion_Character_BP_C",ToClassName="")
NPCReplacements=(FromClassName="MegaRattlesnake_Character_BP_C",ToClassName="")
NPCReplacements=(FromClassName="MegaGiantSnake_Character_BP_C",ToClassName="")
NPCReplacements=(FromClassName="MegaPig_Character_BP_C",ToClassName="")