How to add iTunes blocking tag to the main feed of my site

Hello-

I am using Powerpress to publish a podcast on a client’s website. I made two mistakes. One) I first published it to iTunes using the main feed. 2) realizing my mistake, rather than signalling to iTunes that I had changed the feed, I just republished it under the correct category feed.

So, that 2nd feed is working right, it’s what we need. But the first one needs to go away. I put in a request to iTunes to take it down, but it hasn’t happened yet. When you put in the request, you get a message that says you can just add <iTunes:block> to your feed and they will stop publishing it (which seems to imply that they won’t take it down for you – but I don’t know).

I can’t figure out how to modify the main feed on the site. It says in the codex that WordPress uses formulas to create feeds. I don’t really understand this, but it makes me worry that if I start going into files and adding the <iTunes:block> tag to things, it could put them on other feeds as well. Namely, the one I want to stay up under the category.

So is there a quick way I can modify just the main feed?

Like, if I go to my feed, copy it all off the browser and create a text file with that info and put it in wp-includes? Would that work?

In short: how do I add one measly tag to one measly feed.

[[please note, as I described above, I know there’s a way I SHOULD HAVE done this, but it’s too late and the old feed is already up on iTunes, so I need to get it down]]