It’s not really clear exactly what you’re trying to do, but you might want to check out FDetailArrayBuilder, which makes working with customizations for arrays much easier (e.g., if you want to customize the name of an array entry row to be something more useful than the index of the array entry). There’s an example in FSpriteDetailsCustomization, in order to label the AdditionalTextures array nicely.
RE: The drop-down for add/delete/reset to defaults, that is probably controlled by the ‘bDisplayDefaultPropertyButtons’ parameter of CreatePropertyValueWidget.
Cheers,
Michael Noland