The way the system is designed seems to be that when you define the attribute and its options these are on defaults that will be available when you first attach them to a product, so you're correct in saying that updating attribute option defaults will have no effect on the attribute options you've already attached to products.

The only way I know to do a mass product update like what you're talking about is via sql. It is a pain, but if you're familiar with databases at all it isn't too hard.

Edit: I take that back, I've just looked at the database and see that product attributes and options are stored in different tables (?!), thus making it quite difficult to update via the database. I have no idea why product attributes and options would need to be in seperate tables, options cannot exist without an attribute and attributes have no purpose without options after all.

If they were in the same table it would have been incredibly straight forward. Sorry I can't be of more help.