How do I add a new attribute to many/all products quickly?

[randper]

I am developing a store that has many products that can be customized with various designs (example - tshirts, mugs, plates, mouse pads, etc. with different design options/attributes like: airplane, zoo, zebra, ballerina). Over time, they add designs that would apply to all products. How can I quickly add attributes (designs) that would apply to all items?

Right now, I can do it by going into each item and using the combination generator to add the new attributes, but that's VERY time consuming.