How do you use form customization on GalleryItem Custom TV?

MODX Revolution 2.2.6-pl - Traditional
Gallery 1.5.2

How do you use form customization on GalleryItem Custom TV?

I would like to be able to hide 'other phpthumb options' and 'watermark options'

Can this be done with form customization? or do I have to edit the 'GalleryCustomTV' plugin?

See below
http://rtfm.modx.com/display/ADDON/Gallery.Setting+Up+the+GalleryItem+TV

Thanks
Hope someone can help...