You can disable it by adding this to user.config:

<add key="CombineCSS" value="false"/>​

But generally I advise against doing that. If you tell me why you want to do it I may have better advice for the problem you are trying to solve.

It is not currently possible to replace StyleSheetCombiner with your own thing.

However, it does not have to load lots of css files. Actually StyleSheetCombiner just creates the url for csshandler which combines and minifies the css files. The number of css files is determined only by the list of files in style.config file in the skin folder. If you want fewer files then remove them from style.config or pre-combine the raw css files into fewer files.

Disabling StyleSheetCombiner can be done with the setting I previously provided but all that does is make it create the urls for all the separate css files (listed in style.config) instead of one url for csshandler. Disabling is not recommended because we can only control caching if we use csshandler otherwise the browser may cache the css files. Also disabling it would create lots of urls to the separate files unless you pre-combine then into fewer css files listed in style.config.

Hope that helps,

Joe