Thanks. Hmm, testing right now in the 4 version of plugin and seems the retainer box works as it should. I tested in 3.8 before that.
Anyway, found out how to edit MID's parameters in blueprint, simply exposed array with MIDs. It was easier than I thought :grinteeth:
UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Spine)
TMap<spine::AtlasPage*, UMaterialInstanceDynamic*> pageToNormalBlendMaterial;