I'm not sure, because I haven't done this before, but couldn't you just either send an empty object with setExtraParams() (note the "s" at the end) to reset them? If you want to reset them first and then add a fresh set of params I think you could just send an object with only one property, like so:
Code:
videoStore.getProxy.setExtraParams({}) <-- Reset extraParams
videoStore.getProxy().setExtraParams({ <--- Reset and add a fresh set of params
type: 'article',
type_id: 456
});
I don't know if you just want to reset the extraParams or if you want to reset them before adding new ones, but if it's the latter you can do it as shown in the code above. That should "reset" and add new params, if I'm not mistaken.
EDIT: Do this to reset it: myStore.getProxy().setExtraParams(null). I'm using this myself, so I know it works.