Assigning a custom ability to an Archtype

[ErinRigh]

The class I am working with has a Custom ability category called Maledictions

They gain one at every odd level starting with 1

The archtype I am working on replaces the First level Malediction with a different class ability, Cursed Blade, but allows the archtype to trade in each gained malediction for a this class ability (cursed blade) which stacks with itself

My problem is, I figure it would just be easiest to create the Cursed Blade ability as a Custom ability (Malediction) available only to this archtype, but here are my 2 problems

1) I want to auto assign the Cursed Blade Malediction at 1st level, I can reduce the number of Maledictions easy enough, but I don't know how to make it auto assign the custom ability to the character

2) I don't know how to restrict it to the one archtype