you need to substitute tastic mimetypes in another icon set. E.g. for the faenza icon set you need to convert to png tastic mimetypes ( 16px, 22px, 24px, 32px, 48px) and copy the svgs as they come in the scalable folder. It's necessary to modify a bit the index.theme, renaming the icon set (avoiding duplicates) and changing the dimension of the scalable mimetypes part from 96 to 128.
If you want I can provide you a little script, let me now. thanks