@Idolse - sure, go for it, using whatever means you think appropriate. My hesitation in using cssutils is that (a) I have never used it before, and (b) I am presuming it would result in writing out a completely new css file. Which introduces the "potential" for something else to be changed within it. Maybe it is me being paranoid, but of course the philosophy behind this plugin is to make as minimal changes as is possible to the ePub.
So if you can come up with something that covers all your scenarios and can send it to me that would be great.