Trouble mutating a `SyntaxCollection`

I'm trying to update and replace a specific MemberBlockItemSyntax within a MemberBlockItemListSyntax. This is proving difficult, as some APIs expect Int indexes, and others vend custom index types that don't expose raw integer indexes.

Does anyone have any guidance? :folded_hands:

Can you do the following?

modifiedNodes.memberBlock.members[affectedIndex] = newValue