After doing some testing I have noticed that only replacing the end highlands works

How to replicate:
Make 3 different biomes(so you notice if it works or not)'

Add replacement for the biomes.

TheEndBiomeData.addEndBiomeReplacement(Biomes.END_BARRENS, EQBiomes.END_SEA_BAR_KEY, 5);
TheEndBiomeData.addEndBiomeReplacement(Biomes.END_HIGHLANDS, EQBiomes.END_SEA_KEY, 5);
TheEndBiomeData.addEndBiomeReplacement(Biomes.END_MIDLANDS, EQBiomes.END_SEA_MID_KEY, 5);

When using locate biome only the highlands replacement can be found.
After checking around the world for a bit no other biome other than the highlands replacement was found.