Specify our own defaults for types in drop-down box?

Is there a way to specify additional extensions for specific file types in the drop-down box? For example, I'd like .3gp to be in the "Video" type. I know that I can edit it manually and add it to the list, but sometimes I forget. Is there a way (maybe in the registry?) to let us either modify the search for the predefined types or maybe even add our own types?

I'd just like them to be readily available all the time -- as opposed to me having to manually do them.

Thanks!