Not sure if this is exactly what you are looking for, but Take a look at this: http://help.adobe.com/en_US/flex/using/WS2db454920e96a9e51e63e3d11c0bf69084-7f8c.html#WS2db454920e96a9e51e63e3d11c0bf69084-7e68
From Adobe:
If you have an existing theme SWC file, you can use it as a run-time style sheet. To do this, you must extract the CSS file from the theme SWC file. You then compile the style SWF file by passing the remaining SWC file as a library.
The following steps show this process using the command line:
Extract the CSS file from the SWC file using PKZip or similar archiving utility, as the following example shows:
$ unzip halo.swc defaults.css
(Optional) Rename the CSS file to a meaningful name. This is the name of your style SWF file. The following example renames the defaults.css file to halo.css:
$ mv defaults.css halo.css
Compile the style SWF file. Add the theme SWC file to the style SWF file by using the include-libraries option, as the following example shows:
$ mxmlc -include-libraries=halo.swc halo.css
If you have multiple CSS files inside a theme SWC file, you must extract all of them before compiling the style SWF file.