Hate to tell you this but you probably didn't need to mess with anything in the first place. Sometimes breathers are just noisy... I've never noticed any ill effects from them making a little "squak" I think its just the plastic valve material resonating. If it's cracked it's probably dangerous. I can't tell from the pics but is there any chance it's a scratch? Scratch doesn't matter, crack does.
Personally, and I'm not liable for any personal injuries, but personally I'm a cheap bastard and I'd run it and see what happens, keeping a good distance between me and the engine when it was running at first, just for fun. But if you already ordered a replacement definitely don't risk it.