How can I create an "allow anything" field on a node? We're building a site and need to allow our users to have a field on the node that will allow for ANY content: scripts, iframes, script files, css files, etc; essentially embed codes for mailchimp forms, donation forms, etc.

This HAS to be something the user can do so. Can I create a textarea field and then override a hook or something to prevent that fields contents from going through any sort of filtering?

I also completely understand the risks here. We don't have any public users logging into the site. We know everyone who is logging in.
I would create a new text format for that:


Go to admin/config/content/formats/add
Select the filters you want to add (in your case probably no filters at all)
Add a textarea field on your content type and select this text format you just created.