Possible side effects when changing node type? I sometimes have uses cases where I want to be able to change the type of a node.
There is a nodetype module that comes with a big disclaimer: "only use if you know what you are doing".

Of course I would lose any fields if they have a different name with the other type. What else could go wrong?

Would it be save to use node_load(), modify the type and then use node_save()?
I've changed the content type of nodes directly in the database plenty of times and the only thing I've had to deal with is orphaned field data for nodes.

I think that this orphaned data might cause some false-positive results for certain query types (EntityFieldQuery springs to mind) but I can't be absolutely sure.

Instead of risk this I've always written a small script to go through the field tables in question and clear up any stagnant data after I've made the content type change.

I don't think you'll encounter any errors using node_load() and node_save() as you suggest; it would probably be wise to clear Drupal's cache once you've made the change in case anything needs to be updated there.