How do I change a view pager submit from GET to POST?
You can't POST a link, it's a link; by definition clicking it will send a GET for the target href. The best you could do is hijack the click to POST via JS, set something in the session, then reload the page. Or wrap the View in a form and convert the pager to use submit buttons (possibly styled like links)

But that's very awkward, and would be more than a trivial amount of effort to achieve. Plus you'll need to write a custom Views pager for either method, and you lose the ability to link directly to a certain page, destroying navigation and SEO. 

I would just leave it as it is (ie the same as every pager you're likely to find), or install Views Load More or something, if it's the UI you're concerned about.