After reading a bunch of stuff on this topic I'm finally changing my spark plugs. There are just 2 things I still can't figure out.

First of all, do you absolutely have to take off the 02 sensor to get the plug that is right behind it or can it stay in?

Second, I just pulled one plug and it looks like this......



And I know its Delco and it's a good one, but it looks like it could be the original

So is it a bad thing if I replace it with autolite 104s?