Unfortunately, it is not possible to move posts to/from the Snippets Section. And that kind of goes to the heart of why I like to discourage people from posting to that section unnecessarily: the snippet nodetype is an ugly stepchild, in several ways. For another example, it has no good categorization or indexing system. (That's why I created the New Snippets Index. But being off-site, it is perpetually at risk of de-resolution, just like its predecessor.) The bottom line is that unless you want to depend on unofficial hacks like New Snippets Index, posting to the Snippets Section is almost like dropping your post in a black hole. Snippets also lack certain other niceties we've come to expect in the other sections. For example, as you discovered, a snippet body can contain only a single <code> block. Note that Code Catacombs has similar (but different) oddities which make it somewhat incompatible with the other sections. So, as tye said, for posting a "normal" post for code, CUFP is probably the best choice, except when it's a "fun" post (obfu or poem).

Note - In the interest of full disclosure, you should know that I am largely responsible for the prefatory text of Snippets Section, and although I wrote it in good faith, I can't guarantee that it accurately embodies the opinions of those who set site policy.