Hi kamrann,
as I debugged through all the ue4 code, I finally realized that customizeHeader and customizeChildren are only getting called on initialization anyway. So there can’t exist a way for a simple IPropertyCustomization to get these functions called again.
Although I found the class GameplayEffectModifierMagnitudeDetails.cpp in which delegate functions are used for visibility!
IDetailPropertyRow &row = StructBuilder.AddChildProperty(ChildHandle.ToSharedRef()); //add default property representation
row.Visibility(TAttribute<EVisibility>::Create(TAttribute<EVisibility>::FGetter::CreateSP(this, &FActionCustomization::PropertyIsVisible, ChildHandle->GetProperty(), &row)));
Using this delegate function now works perfectly, as these delegate functions are called each update frame in UE4.
Thanks for the hints!