I'd argue that this is a style choice, though I personally would put a comma.
I would argue that it's not a style choice because it's an introductory phrase.
I believe that "Structural Amendments" was treated as Amendment IX (much as "Omnibus Amendments" was treated as Amendment I).
I thought that too at first, but there are some other amendments to it in between that don't have numbers and don't offset the other Amendments' numbers.