I downloaded a model (this one, actually http://www.blendswap.com/blends/view/70898) for practicing animation purposes, but i want to add some few features, like sleeves or a nose (because the character doesn't have one) to also practice about textures, so for example i would be able to add a shirt eventhough i can already add one with a plain image alongside the body of the character...but as i said on the title of this question ,the model is already rigged, working with bones, if for example i extrude part of the face of the character, it will be deformed badly and it will appear pretty bad on render, for example, how can i modify simple features without modifing the rig?
I do not only ask this about this model, but of any other model for future reference, i can also rig characters but what if for example, same as this example, i want to modify an already made character that works perfectly with the bones?