So you want to change the Facebook Page to something that is not listed in the Page category dropdown? I will show you step by step how to do this.
Long story short - what you have to do is to make the About setting form to reveal the Sub-category setting. This often reqires to "unlock" the Address setting first and add a valid address. I will show this on an example with a Page set up as a "Concert Tour" category, but It's applicable to any other setting.
1/ I have a page under "Concert Tour" category and I'm not happy with it, as it's a page for a music festival. The closest category to music festival in the available list is an "Event". I will want to change the page to this. In the initial stage, I have no way to do it, as the "Event" category is not listed.
So what exactly is there to choose from? This is a list taken on January 2015, the updated list can be pulled from Facebook in Graph API Explorer with the query
P.S.: don't forget to visit our psytrance festival UFO BUFO Facebook page, which is finally tagged as an "Event", not a "Concert Tour".. ;)