Altering the config does not alters yellorite generation, and nothing else in the pack does yellorite generation.

Setting it to require steel, still requires iron.

The part of the config:
recipes {
B:enableCyaniteFromYelloriumRecipe=true
B:enableReactorPowerTapRecipe=true
B:registerCharcoalForSmelting=true
B:registerCoalForSmelting=true
B:registerGraphiteCharcoalCraftingRecipes=false
B:registerGraphiteCoalCraftingRecipes=false
B:registerYelloriteSmeltToUranium=true
B:registerYelloriumAsUranium=true
B:requireObsidianGlass=true
B:requireSteelInsteadOfIron=true
}

worldgen

worldgen {
B:GenerateYelloriteOre=true
I:MaxYelloriteClustersPerChunk=2
I:MaxYelloriteOrePerCluster=1
I:YelloriteClustersPerChunk=1
I:YelloriteDimensionBlacklist <
>
I:YelloriteMaxY=50
D:YelloriteOreGenBaseChance=0.75
D:YelloriteOreGenChanceMultiplier=0.5
I:YelloriteOrePerCluster=1
B:enableWorldGen=true
B:enableWorldGenInNegativeDims=false
B:enableWorldRegeneration=false
I:userWorldGenVersion=0

Latest 1.6.4.

Sorry, this works for me. I suspect you're not saving the file properly or something.