It's global for each method as it's defined in the module, but for flatrate and weightquote, they're simple enough that you can copy them and change the shipping type to whatever you need. If you need a new shipping type, you can make one with hook_shipping_type(). See uc_quote or uc_ups for examples. Since they all use the same shipping type, they all define it the same way. With one new module, you can make a new shipping type and a new shipping method to for each one.