Editing Footer

I’m attempting to edit my footer but am not able to do so without breaking the site.

Ultimately, I want to edit the text (obviously) but also add an email opt-in for some/all of the pages.

I’ve used the code from http://my.studiopress.com/snippets/footer/#credits (as recommended in an older post) in my functions.php but every time I add it my site will break and I have to open up the functions.php in a text editor to delete it.

I’m not clear on why this might be happening. Any thoughts?