I would not set this up as a single test with multiple pages. Otherwise, you'll have visitors "enter" that don't even click the button and therefore do not really participate in the test, but will impact the numbers of your test.
I'd setup a "helper" activity to change the button link, adding some query param to the link for the entry conditions of the real test.
Setup a second activity (the real AB test) - use XT type, create an audience for the default link, and an audience for the exp B link. On exp B you make the content changes to the page. Add your metrics and here you'll have reporting that only applies to people who actually participate in the test.
The helper does your traffic splitting and allows you to modify the button links without using a redirect test.